Editing Fortification

{{Use American English|date=January 2025}}
{{Use mdy dates|date=January 2025}}
{{Short description|Military defensive construction}}
{{Redirect-several|Fort|Fortress|Stronghold|Fortification}}
{{Distinguish|food fortification|fortified wine}}
{{more citations needed|date=January 2013}}
{{War}}
[[File:Castillo San Felipe del Morro (10 of 1).jpg|thumb|[[Castillo San Felipe del Morro]], Puerto Rico. The fortress and walled city of [[Old San Juan]] are a UNESCO [[World Heritage Site]].]]

A '''fortification''' (also called a '''fort''', '''fortress''', '''fastness''', or '''stronghold''') is a [[military]] [[construction]] designed for the defense of territories in [[war]]fare, and is used to establish rule in a region during [[peacetime]]. The term is derived from [[Latin]] {{lang|la|fortis}} ("strong") and {{lang|la|facere}} ("to make").{{sfn|Jackson|1911|p=679}}

[[File:Aerial photograph of Maiden Castle, 1935.jpg|thumb|[[Maiden Castle, Dorset|Maiden Castle]] in 1935. The [[Iron Age]] [[hillfort]] was first built in 600 BC.]]

From very early history to modern times, [[defensive wall]]s have often been necessary for cities to survive in an ever-changing world of [[invasion]] and [[conquest]]. Some settlements in the [[Indus Valley Civilization]] were the first small cities to be fortified. In [[ancient Greece]], large [[cyclopean]] stone walls fitted without mortar had been built in [[Mycenaean Greece]], such as the ancient site of [[Mycenae]]. A Greek ''[[Towns of ancient Greece#Military settlements|phrourion]]'' was a fortified collection of buildings used as a military [[garrison]], and is the equivalent of the [[ancient Roman|Roman]] [[castellum]] or fortress. These constructions mainly served the purpose of a watch tower, to guard certain roads, passes, and borders. Though smaller than a real fortress, they acted as a border guard rather than a real strongpoint to watch and maintain the border.

The art of setting out a military camp or constructing a fortification traditionally has been called "castrametation" since the time of the [[Roman legion]]s. Fortification is usually divided into two branches: permanent fortification and field fortification. There is also an intermediate branch known as semipermanent fortification.{{sfn|Jackson|1911|p=680}} [[Castle]]s are fortifications which are regarded as being distinct from the generic fort or fortress in that they are a residence of a [[monarch]] or [[Nobility|noble]] and command a specific defensive territory.

[[Castra|Roman forts]] and [[hill fort]]s were the main antecedents of castles in Europe, which emerged in the 9th century in the [[Carolingian Empire]]. The [[Early Middle Ages]] saw the creation of some towns built around castles.

Medieval-style fortifications were largely made obsolete by the arrival of [[cannon]]s in the 14th century. Fortifications in the age of [[black powder]] evolved into much lower structures with greater use of [[Ditch (fortification)|ditches]] and [[Earthworks (engineering)|earth]] [[Rampart (fortification)|ramparts]] that would absorb and disperse the energy of cannon fire. Walls exposed to direct cannon fire were very vulnerable, so the walls were sunk into ditches fronted by earth slopes to improve protection.

The arrival of [[explosive shell]]s in the 19th century led to another stage in the evolution of fortification. [[Star fort]]s did not fare well against the effects of high explosives, and the intricate arrangements of bastions, flanking batteries and the carefully constructed lines of fire for the defending cannon could be rapidly disrupted by explosive shells. [[Steel]]-and-[[concrete]] fortifications were common during the 19th and early 20th centuries. The advances in modern warfare since [[World War I]] have made large-scale fortifications obsolete in most situations.

==History==

===Early uses===
[[File:Han Tomb Brick - 3.jpg|thumb|[[Han dynasty]] tomb brick showing gate towers]]

Defensive fences for protecting humans and domestic animals against predators was used long before the appearance of writing and began "perhaps with primitive man blocking the entrances of his [[Cave|caves]] for security from large [[Carnivore|carnivores]]".<ref>{{cite web |last1=A. Wade |first1=Dale |title=THE USE OF FENCES FOR PREDATOR DAMAGE CONTROL |url=https://core.ac.uk/reader/188047270 |website=University of Nebraska - Lincoln |publisher=Wade, Dale A., "THE USE OF FENCES FOR PREDATOR DAMAGE CONTROL" (1982). Proceedings of the Tenth Vertebrate Pest Conference (1982). 47. |access-date=19 September 2024}}</ref>

From very early history to modern times, [[Defensive wall|walls]] have been a necessity for many cities. [[Amnya Fort]] in western Siberia has been described by archeologists as one of the oldest known fortified settlements, as well as the northernmost Stone Age fort.<ref>{{cite journal |last1=Piezonka |first1=Henny |last2=Chairkina |first2=Natalya |last3=Dubovtseva |first3=Ekaterina |last4=Kosinskaya |first4=Lyubov |last5=Meadows |first5=John |last6=Schreiber |first6=Tanja |date=December 1, 2023 |title=The world's oldest-known promontory fort: Amnya and the acceleration of hunter-gatherer diversity in Siberia 8000 years ago |url=https://www.cambridge.org/core/journals/antiquity/article/worlds-oldestknown-promontory-fort-amnya-and-the-acceleration-of-huntergatherer-diversity-in-siberia-8000-years-ago/90559E4105F93528A6552B36C7236259 |journal=[[Antiquity (journal)|Antiquity]] |volume=97 |issue=396|pages=1381–1401 |doi=10.15184/aqy.2023.164 |doi-access=free }}</ref> In Bulgaria, near the town of [[Provadia]] a walled fortified settlement today called [[Solnitsata]] starting from 4700 BC had a diameter of about {{convert|300|ft}}, was home to 350 people living in two-story houses, and was encircled by a fortified wall. The huge walls around the settlement, which were built very tall and with stone blocks which are {{convert|6|ft|sp=us}} high and {{convert|4.5|ft|sp=us}} thick, make it one of the earliest walled settlements in Europe<ref>{{cite web |url=http://www.nbcnews.com/id/49645182 |archive-url=https://web.archive.org/web/20200402235426/http://www.nbcnews.com/id/49645182 |url-status=dead |archive-date=April 2, 2020 |title=Bulgaria claims to find Europe's oldest town  |work=NBC News |date=2012-11-01 |access-date=2013-05-04 }}</ref><ref>{{cite news |url=https://www.bbc.co.uk/news/world-europe-20156681 |title= Europe's oldest prehistoric town unearthed in Bulgaria |publisher=Bbc.co.uk |date=2012-10-31 |access-date=2013-05-04 |url-status=live |archive-url=https://web.archive.org/web/20130611222256/http://www.bbc.co.uk/news/world-europe-20156681 |archive-date=2013-06-11 |work=BBC News }}</ref> but it is younger than the walled town of [[Sesklo]] in Greece from 6800 BC.<ref>{{cite web |url=http://www.greek-thesaurus.gr/neolithic-settlements-organization.html |title=Organization of neolithic settlements:house construction |publisher=Greek-thesaurus.gr |access-date=2013-05-04 |url-status=live |archive-url=https://web.archive.org/web/20130722215151/http://www.greek-thesaurus.gr/neolithic-settlements-organization.html |archive-date=2013-07-22 }}</ref><ref>{{cite web |url=http://odysseus.culture.gr/h/3/eh351.jsp?obj_id=2500 |title=Hellenic Ministry of Culture and Tourism &#124; Sesklo |publisher=Odysseus.culture.gr |access-date=2013-05-04 |url-status=live |archive-url=https://web.archive.org/web/20130102060412/http://odysseus.culture.gr/h/3/eh351.jsp?obj_id=2500 |archive-date=2013-01-02 }}</ref>

[[Uruk]] in ancient [[Sumer]] ([[Mesopotamia]]) is one of the world's oldest known [[walled cities]]. The Ancient Egyptians also built fortresses on the frontiers of the [[Nile Valley]] to protect against invaders from adjacent territories, as well as circle-shaped mud brick walls around their cities. Many of the fortifications of the ancient world were built with mud brick, often leaving them no more than mounds of dirt for today's archeologists. A massive prehistoric stone wall surrounded the ancient temple of [[Ness of Brodgar]] 3200 BC in [[Scotland]]. Named the "Great Wall of Brodgar" it was {{convert|4|m|ft|sp=us|abbr=on}} thick and {{convert|4|m|ft|sp=us|abbr=on}} tall. The wall had some symbolic or ritualistic function.<ref>{{cite web |author=The Ness of Brodgar Excavations |url=http://www.orkneyjar.com/archaeology/nessofbrodgar/excavation-background-2/the-great-wall-of-brodgar/ |title=The Ness of Brodgar Excavations – The 'Great Wall of Brodgar' |publisher=Orkneyjar.com |access-date=2013-05-04 |url-status=live |archive-url=https://web.archive.org/web/20130428094607/http://www.orkneyjar.com/archaeology/nessofbrodgar/excavation-background-2/the-great-wall-of-brodgar/ |archive-date=2013-04-28 }}</ref><ref>{{cite web |author=Alex Whitaker |url=http://www.ancient-wisdom.co.uk/scotlandness.htm |title=The Ness of Brodgar |publisher=Ancient-wisdom.co.uk |access-date=2013-05-04 |url-status=live |archive-url=https://web.archive.org/web/20130501034018/http://www.ancient-wisdom.co.uk/scotlandness.htm |archive-date=2013-05-01 }}</ref> The [[ancient Assyrians|Assyrians]] deployed large labor forces to build new [[palaces]], temples and defensive walls.<ref>{{cite book |title=Sir Banister Fletcher's A History of Architecture |first1=Banister |last1=Fletcher |first2=Dan |last2=Cruickshank |date=1996 |publisher=Architectural Press |isbn=0-7506-2267-9 |page=20}}</ref>

===Bronze Age Europe===
[[File:Borg in-Nadur ruins.jpeg|thumb|left|Remains of a fortified village, [[Borġ in-Nadur]], Malta. Borġ in-Nadur is a notable example of [[Bronze Age]] fortifications.]]

In [[Bronze Age]] [[Malta (island)|Malta]], some settlements also began to be fortified. The most notable surviving example is [[Borġ in-Nadur]], where a bastion built in around 1500 BC was found. Exceptions were few—notably, ancient [[Sparta]] and ancient [[Rome]] did not have walls for a long time, choosing to rely on their militaries for defense instead. Initially, these fortifications were simple constructions of wood and earth, which were later replaced by mixed constructions of stones piled on top of each other without [[Mortar (masonry)|mortar]]. In [[ancient Greece]], large stone walls had been built in [[Mycenaean Greece]], such as the ancient site of [[Mycenae]] (famous for the huge stone blocks of its '[[cyclopean]]' walls). In [[Classical Greece|classical era Greece]], the city of [[Athens]] built two parallel stone walls, called the [[Long Walls]], that reached their fortified seaport at [[Piraeus]] a few miles away.

In [[Central Europe]], the [[Celts]] built large fortified settlements known as [[oppidum|oppida]], whose walls seem partially influenced by those built in the [[Mediterranean]]. The fortifications were continuously being expanded and improved. Around 600 BC, in [[Heuneburg]], Germany, forts were constructed with a limestone foundation supported by a [[mudbrick]] wall approximately 4 meters tall, probably topped by a roofed walkway, thus reaching a total height of 6 meters. The wall was clad with lime plaster, regularly renewed. Towers protruded outwards from it.<ref>{{cite web|last1=Focke|first1=Arne|title=Die Heuneburg an der oberen Donau: Die Siedlungsstrukturen|url=http://www.isentosamballerer.de/de/bibliothek/siedlungsstrukturen-heuneburg/befestigungen.html|website=isentosamballerer.de|date=2006|language=de}}{{dead link|date=August 2016|bot=medic}}{{cbignore|bot=medic}}</ref><ref>{{cite web|title=Erforschung und Geschichte der Heuneburg|url=http://www.heuneburg.de/heuneburg-kelten.htm|website=Celtic Museum Heuneburg|archive-url=https://web.archive.org/web/20070624231023/http://www.heuneburg.de/heuneburg-kelten.htm|archive-date=24 June 2007|language=de}}</ref>
[[File:Bibracte Porte Rebout.jpg|thumb|Reconstructed walls of [[Bibracte]], a [[Gaulish]] ''[[oppidum]]'', showing the construction technique known as ''[[Murus Gallicus|murus gallicus]]''. ''Oppida'' were large fortified settlements used during the [[Iron Age]].]]

The [[Oppidum of Manching]] (German: Oppidum von Manching) was a large Celtic proto-urban or city-like settlement at modern-day Manching (near Ingolstadt), Bavaria (Germany). The settlement was founded in the 3rd century BC and existed until {{Circa|50–30 BC}}. It reached its largest extent during the late La Tène period (late 2nd century BC), when it had a size of 380 hectares. At that time, 5,000 to 10,000 people lived within its 7.2&nbsp;km long walls. The oppidum of [[Bibracte]] is another example of a Gaulish fortified settlement.

===Bronze and Iron Age Near East===
{{See also|Casemate}}
[[File:Casamata de Masada.jpg|thumb|right|An ancient casemate wall at [[Masada]].]]

The term ''casemate wall'' is used in the archeology of [[Land of Israel|Israel]] and the wider [[Near East]], having the meaning of a double wall protecting a city<ref name=Safra>{{cite web |last=Emswiler |first=Elizabeth Anne |title=The Casemate Wall System of Khirbat Safra |pages=1, 3–15 |date=2020 |publisher=[[Andrews University]] |url=https://digitalcommons.andrews.edu/cgi/viewcontent.cgi?article=1156&context=theses |access-date=22 October 2021}}</ref> or fortress,<ref name=MGH>{{cite dictionary |title=Casemate wall |dictionary =McGraw-Hill Dictionary of Architecture and Construction |publisher=[[McGraw-Hill]] |via=[[The Free Dictionary]] |url=https://encyclopedia2.thefreedictionary.com/casemate+wall |access-date=16 July 2022}}</ref> with transverse walls separating the space between the walls into chambers.<ref name=Safra /> These could be used as such, for storage or residential purposes, or could be filled with soil and rocks during siege in order to raise the resistance of the outer wall against battering rams.<ref name=Safra /> Originally thought to have been introduced to the region by the [[Hittites]], this has been disproved by the discovery of examples predating their arrival, the earliest being at [[Ti'inik]] (Taanach) where such a wall has been dated to the [[16th century BC]].<ref>Emswiler (2020), pp. 7–9.</ref> Casemate walls became a common type of fortification in the Southern Levant between the Middle Bronze Age (MB) and Iron Age II, being more numerous during the Iron Age and peaking in Iron Age II (10th–6th century BC).<ref name=Safra /> However, the construction of casemate walls had begun to be replaced by sturdier solid walls by the [[9th century BC]], probably due the development of more effective battering rams by the [[Neo-Assyrian Empire]].<ref name=Safra /><ref name=EB>{{cite encyclopedia |author=[[Seton Lloyd|Lloyd, Seton H.F.]]  |title=Syro-Palestinian art and architecture |encyclopedia=[[Encyclopædia Britannica]] |via= Britannica Online |url=https://www.britannica.com/art/Syro-Palestinian-art#ref419785 |access-date=16 July 2022}}</ref> Casemate walls could surround an entire settlement, but most only protected part of it.<ref>Emswiler (2020), p. 4.</ref> The three different types included freestanding casemate walls, then integrated ones where the inner wall was part of the outer buildings of the settlement, and finally filled casemate walls, where the rooms between the walls were filled with soil right away, allowing for a quick, but nevertheless stable construction of particularly high walls.<ref>Emswiler (2020), pp. 4–5.</ref>

===Ancient Rome===
{{Main|Roman military frontiers and fortifications}}
[[File:Celio - le mura tra porta san Sebastiano e porta Ardeatina 2004.JPG|thumb|An interior view of the [[Aurelian walls]] near [[Porta San Sebastiano]]]]

The [[ancient Rome|Romans]] fortified their cities with massive, mortar-bound stone walls. The most famous of these are the largely extant [[Aurelian Walls]] of [[Rome]] and the [[Theodosian Walls]] of [[Constantinople]], together with partial remains elsewhere. These are mostly city gates, like the [[Porta Nigra]] in [[Trier]] or [[Newport Arch]] in [[Lincoln, Lincolnshire|Lincoln]]. 

[[Hadrian's Wall]] was built by the [[Roman Empire]] across the width of what is now [[northern England]] following a visit by [[List of Roman Emperors|Roman Emperor]] [[Hadrian]] (AD&nbsp;76–138) in AD&nbsp;122.

===Indian subcontinent===
{{Main|Forts in India|List of forts in India|List of forts in Pakistan|List of forts in Nepal}}
[[File:Dholavira gujarat.jpg|thumb|Defensive wall of the ancient city of [[Dholavira]], Gujarat 2600 BCE]]

A number of forts dating from the [[Later Stone Age]] to the [[British Raj]] are found in the mainland [[Indian subcontinent]] (modern day [[India]], [[Pakistan]], [[Bangladesh]] and [[Nepal]]). "Fort" is the word used in India for all old fortifications. Numerous [[Indus Valley civilisation|Indus Valley Civilization]] sites exhibit evidence of fortifications. By about 3500 BC, hundreds of small farming villages dotted the [[Indus]] floodplain. Many of these settlements had fortifications and planned streets. The stone and mud brick houses of [[Kot Diji]] were clustered behind massive stone flood dykes and defensive walls, for neighboring communities bickered constantly about the control of prime agricultural land.<ref>{{cite book |title=The Encyclopedia of World History: ancient, medieval, and modern, chronologically arranged  |first1=Peter N. |last1=Stearns |first2=William Leonard |last2=Langer |date=2001 |publisher=Houghton Mifflin Books |isbn=0-395-65237-5 |page=17}}</ref> The fortification varies by site. While  [[Dholavira]] has stone-built fortification walls, [[Harappa|Harrapa]] is fortified using baked bricks; sites such as [[Kalibangan]] exhibit [[mudbrick]] fortifications with bastions and [[Lothal]] has a quadrangular fortified layout. Evidence also suggested of fortifications in [[Mohenjo-daro]]. Even a small town—for instance, Kotada Bhadli, exhibiting sophisticated fortification-like bastions—shows that nearly all major and minor towns of the Indus Valley Civilization were fortified.<ref>{{Cite web|url=https://openaccess.leidenuniv.nl/bitstream/handle/1887/19437/Agressive%20Architecture.pdf?sequence=1|title=Agressive Architecture: Fortifications of the Indus Valley in the Mature Harappan phase &#124; Student Repository}}</ref> Forts also appeared in urban cities of the Gangetic valley during the second urbanization period between 600 and 200 BC, and as many as 15 fortification sites have been identified by archeologists throughout the Gangetic valley, such as [[Kosambi|Kaushambi]], [[Mahasthangarh]], [[Pataliputra]], [[Mathura]], [[Ahichchhatra]], [[Rajgir]], and [[Lauria Nandangarh]]. The earliest [[Maurya Empire|Mauryan period]] brick fortification occurs in one of the stupa mounds of Lauria Nandangarh, which is 1.6&nbsp;km in perimeter and oval in plan and encloses a habitation area.<ref>{{Cite journal|last=Barba|first=Federica|date=2004|title=The Fortified Cities of the Ganges Plain in the First Millennium B.C.|journal=East and West|volume=54|issue=1/4|pages=223–250|jstor=29757611}}</ref>[[Mundigak]] ({{Circa|2500 BC}}) in present-day south-east [[Afghanistan]] has defensive walls and square [[bastion]]s of sun dried bricks.<ref>{{cite book |title=Sir Banister Fletcher's A History of Architecture |first1=Banister |last1=Fletcher |first2=Dan |last2=Cruickshank |date=1996 |publisher=Architectural Press |isbn=0-7506-2267-9 |page=100}}</ref>
[[File:Jaisalmer forteresse.jpg|thumb|[[Jaisalmer Fort]], [[Rajasthan]], India]]

India currently has over 180 forts, with the state of [[Maharashtra]] alone having over 70 forts, which are also known as ''durg'',<ref>''Durga'' is the [[Sanskrit]] word for "inaccessible place", hence "fort"</ref><ref name="Nossov-8"/><ref>{{Cite book |last=Hiltebeitel |first=Alf |author-link=Alf Hiltebeitel |year=1991 |title=The Cult of Draupadī: Mythologies: From Gingee to Kurukserta |location=Delhi, India |publisher=Motilal Banarsidass |volume=1 |page=[https://books.google.com/books?id=VncomfRVVhoC&pg=PA62 62] |isbn=978-81-208-1000-6}}</ref> many of them built by [[Shivaji]], founder of the [[Maratha Confederacy|Maratha Empire]].

A large majority of forts in India are in North India. The most notable forts are the [[Red Fort]] at [[Old Delhi]], the [[Agra Fort|Red Fort]] at [[Agra]], the [[Chittor Fort]] and [[Mehrangarh Fort]] in [[Rajasthan]], the [[Ranthambhor Fort]], [[Amer Fort]] and [[Jaisalmer Fort]] also in Rajasthan and [[Gwalior Fort]] in [[Madhya Pradesh]].<ref name="Nossov-8">{{Cite book|author=Nossov, Konstantin|year=2012|title=Indian Castles 1206–1526: The Rise and Fall of the Delhi Sultanate|edition=second|location=Oxford|publisher=Osprey Publishing|page=[https://books.google.com/books?id=pMydaF1yzM8C&pg=PA8 8]|isbn=978-1-78096-985-5}}</ref>

[[Arthashastra]], the Indian treatise on military strategy describes six major types of forts differentiated by their major modes of defenses.

==== Sri Lanka ====
{{Main|Forts in Sri Lanka}}
[[File:Beauty of Sigiriya by Binuka.jpg|thumb|Rock fort of [[Sigiriya]] built by King [[Kashyapa I of Anuradhapura]].]]

Forts in [[Sri Lanka]] date back thousands of years, with many being built by Sri Lankan kings. These include several walled cities. With the outset of colonial rule in the [[Indian Ocean]], Sri Lanka was occupied by several major colonial empires that from time to time became the dominant power in the Indian Ocean. The colonists built several western-style forts, mostly in and around the coast of the island. The first to build colonial forts in Sri Lanka were the [[Portuguese Empire|Portuguese]]; these forts were captured and later expanded by the [[Dutch colonial empire|Dutch]]. The [[British Empire|British]] occupied these Dutch forts during the [[Napoleonic wars]]. Most of the colonial forts were garrisoned up until the early 20th century. The coastal forts had [[coastal artillery]] manned by the [[Ceylon Garrison Artillery]] during the two world wars.
Most of these were abandoned by the military but retained civil administrative officers, while others retained military garrisons, which were more administrative than operational. Some were reoccupied by military units with the escalation of the [[Sri Lankan civil war|Sri Lankan Civil War]]; [[Jaffna fort]], for example, came under siege several times.

===China===
{{See also|Chinese city wall|List of castles in China}}
[[File:20090529 Great Wall 8185.jpg|thumb|The [[Great Wall of China]] near [[Jinshanling]]. The Great Wall was a series of fortifications built across the historical northern borders of China. ]]

Large tempered earth (i.e. [[rammed earth]]) walls were built in [[ancient China]] since the [[Shang dynasty]] ({{Circa|1600}}–1050 BC); the capital at ancient Ao had enormous walls built in this fashion (see [[siege]] for more info). Although stone walls were built in China during the [[Warring States]] (481–221 BC), mass conversion to stone architecture did not begin in earnest until the [[Tang dynasty]] (618–907 AD). The [[Great Wall of China]] had been built since the [[Qin dynasty]] (221–207 BC), although its present form was mostly an engineering feat and remodeling of the [[Ming dynasty]] (1368–1644 AD).

In addition to the Great Wall, a number of Chinese cities also employed the use of [[defensive wall]]s to defend their cities. Notable [[Chinese city wall]]s include the city walls of [[Hangzhou City Walls|Hangzhou]], [[City Wall of Nanjing|Nanking]], the [[Old City (Shanghai)|Old City of Shanghai]], [[City Wall of Suzhou|Suzhou]], [[Fortifications of Xi'an|Xi'an]] and the [[walled villages of Hong Kong]]. The famous walls of the [[Forbidden City]] in [[Beijing]] were established in the early 15th century by the [[Yongle Emperor]]. The Forbidden City made up the inner portion of the [[Beijing city fortifications]].

===Philippines===

====Spanish colonial fortifications====
{{Main|Spanish colonial fortifications in the Philippines}}

During the [[Spanish East Indies|Spanish Era]] several forts and outposts were built throughout the archipelago. Most notable is [[Intramuros]], the old [[defensive walls|walled]] city of Manila located along the southern bank of the [[Pasig River]].<ref>Luengo, Pedro. Intramuros: Arquitectura en Manila, 1739–1762. Madrid: Fundacion Universitaria Española, 2012</ref> The historic city was home to centuries-old churches, schools, convents, government buildings and residences, the best collection of Spanish colonial architecture before much of it was destroyed by the bombs of [[World War II]]. Of all the buildings within the 67-acre city, only one building, the San Agustin Church, survived the war.

Partial listing of Spanish forts:
# [[Intramuros]], Manila
# [[Cuartel de Santo Domingo]], Santa Rosa, Laguna
# [[Cuyo Fort|Fuerza de Cuyo]], Cuyo, Palawan
# [[Cagayancillo Fort|Fuerza de Cagayancillo]], Cagayancillo, Palawan
# [[Fort Pilar|Real Fuerza de Nuestra Señora del Pilar de Zaragoza]], Zamboanga City
# [[Fort San Felipe (Cavite)|Fuerza de San Felipe]], Cavite City
# [[Fort San Pedro|Fuerza de San Pedro]], Cebu
# [[Fuerte de la Concepcion y del Triunfo]], Ozamiz, Misamis Occidental
# [[Fort San Antonio Abad|Fuerza de San Antonio Abad]], Manila
# [[Fort Pikit|Fuerza de Pikit]], Pikit, Cotabato
# Fuerza de Santiago, [[Romblon, Romblon]]
# Fuerza de Jolo, [[Jolo, Sulu]]
# Fuerza de Masbate, [[Masbate]]
# Fuerza de Bongabong, [[Bongabong, Oriental Mindoro]]
# Cotta de Dapitan, [[Dapitan]], Zamboanga del Norte
# Fuerte de Alfonso XII, [[Tukuran, Zamboanga del Sur]]
# Fuerza de Bacolod, [[Bacolod, Lanao del Norte]]
# Guinsiliban Watchtower, [[Guinsiliban, Camiguin]]
# Laguindingan Watchtower, [[Laguindingan, Misamis Oriental]]
# Kutang San Diego, [[Gumaca, Quezon]]
# Baluarte Luna, [[Luna, La Union]]

====Local fortifications====
{{Main|Ivatan people|Architecture of the Philippines}}

The Ivatan people of the northern islands of Batanes built their so-called ''[[idjang]]'' on hills and elevated areas<ref>{{cite web|url=http://www.filipiknow.net/archaeological-discoveries-in-the-philippines/|title=15 Most Intense Archaeological Discoveries in Philippine History|work=FilipiKnow|access-date=17 March 2015|url-status=live|archive-url=https://web.archive.org/web/20150315060732/http://www.filipiknow.net/archaeological-discoveries-in-the-philippines/|archive-date=15 March 2015}}</ref> to protect themselves during times of war. These fortifications were likened to European castles because of their purpose. Usually, the only entrance to the castles would be via a rope ladder that would only be lowered for the villagers and could be kept away when invaders arrived.
[[File:American flag raised over Fort Santiago 8-13-1898.jpg|thumb|left|An American flag raised at the [[Fort Santiago]], 1898. Fort Santiago was a [[citadel]] that was a part of the [[Intramuros]], a walled city within Manila.]]

The [[Igorot people|Igorots]] built forts made of stone walls that averaged several meters in width and about two to three times the width in height around 2000 BC.<ref name="irwin">[http://www.livecebu.com/philhistory.htm#Ancientprspanish Ancient and Pre-Spanish Era of the Philippines] {{webarchive|url=https://web.archive.org/web/20151210190659/http://livecebu.com/philhistory.htm |date=2015-12-10 }}. Accessed September 04, 2008.</ref>

The Muslim Filipinos of the south built strong [[fortresses]] called ''kota'' or ''moong'' to protect their communities. Usually, many of the occupants of these kotas are entire families rather than just warriors. Lords often had their own kotas to assert their right to rule, it served not only as a military installation but as a palace for the local Lord. It is said that at the height of the [[Sultanate of Maguindanao|Maguindanao Sultanate]]'s power, they blanketed the areas around Western [[Mindanao]] with kotas and other fortifications to block the Spanish advance into the region. These kotas were usually made of stone and bamboo or other light materials and surrounded by trench networks. As a result, some of these kotas were burned easily or destroyed. With further Spanish campaigns in the region, the sultanate was subdued and a majority of kotas dismantled or destroyed. kotas were not only used by the Muslims as defense against Spaniards and other foreigners, renegades and rebels also built fortifications in defiance of other chiefs in the area.{{citation needed|date=January 2023}} During the American occupation, rebels built strongholds and the datus, rajahs, or sultans often built and reinforced their kotas in a desperate bid to maintain rule over their subjects and their land.<ref>{{cite web|url=http://www.morolandhistory.com/08.PG-Battle%20of%20Bayan/battle_of_bayan_p2.htm|title=The Battle of Bayan|access-date=17 March 2015|url-status=dead|archive-url=https://web.archive.org/web/20151230005052/http://www.morolandhistory.com/08.PG-Battle%20of%20Bayan/battle_of_bayan_p2.htm|archive-date=2015-12-30}}</ref> Many of these forts were also destroyed by American expeditions, as a result, very very few kotas still stand to this day.

Notable kotas:
* [[Kingdom of Maynila|Kota Selurong]]: an outpost of the [[Bruneian Empire]] in Luzon, later became the City of [[Manila]].
* [[Cotabato City|Kuta Wato/Kota Bato]]: Literally translates to "stone fort" the first known stone fortification in the country, its ruins exist as the "Kutawato Cave Complex"<ref>{{cite web|url=http://www.cotabatocity.net.ph/index.php?option=com_content&view=article&id=69&Itemid=79&limitstart=1|title= The Kutawato Caves|access-date=17 March 2015|url-status=live|archive-url=https://web.archive.org/web/20141016065601/http://www.cotabatocity.net.ph/index.php?option=com_content&view=article&id=69&Itemid=79&limitstart=1|archive-date=16 October 2014}}</ref>
* [[Jolo, Sulu|Kota Sug/Jolo]]: The capital and seat of the [[Sultanate of Sulu]]. When it was occupied by the Spaniards in the 1870s they converted the kota into the world's smallest walled city.

===Pre-Islamic Arabia===

====During Muhammad's lifetime====
{{Main|List of expeditions of Muhammad}}
[[File:The Battle of the Trench.jpg|thumb|Map of defenses available during the [[Battle of the Trench]], 627. Muslim defenders repelled the Confederates using Medina's natural fortifications and makeshift trenches.]]

During [[Muhammad]]'s era in Arabia, many tribes made use of fortifications. In the [[Battle of the Trench]], the largely outnumbered defenders of Medina, mainly [[Muslim]]s led by [[Prophets of Islam|Islamic prophet]] Muhammad, dug a [[Trench warfare|trench]], which together with Medina's natural fortifications, rendered the confederate [[cavalry]] (consisting of horses and [[Camel cavalry|camels]]) useless, locking the two sides in a stalemate. Hoping to make several attacks at once, the confederates persuaded the Medina-allied [[Banu Qurayza]] to attack the city from the south. However, [[Muhammad as a diplomat|Muhammad's diplomacy]] derailed the negotiations, and broke up the confederacy against him. The well-organized defenders, the sinking of confederate morale, and poor weather conditions caused the siege to end in a fiasco.<ref name =statesman>*{{cite book | last = Watt |first=William M. | author-link = William Montgomery Watt | title = Muhammad: Prophet and Statesman | publisher = [[Oxford University Press]] | year = 1974 | isbn = 978-0-19-881078-0 | page = [https://archive.org/details/muhammadprophets00watt/page/96 96] | url = https://archive.org/details/muhammadprophets00watt/page/96 }}</ref>

During the [[Siege of Ta'if]] in January 630,<ref name="Mubarakpuri 2005 481">{{citation|title=The sealed nectar: biography of the Noble Prophet|url=https://books.google.com/books?id=r_80rJHIaOMC&pg=PA481|first=Saifur Rahman Al|last=Mubarakpuri|year=2005|publisher=Darussalam Publications|isbn=978-9960-899-55-8|page=481|url-status=live|archive-url=https://web.archive.org/web/20160419104753/https://books.google.com/books?id=r_80rJHIaOMC&pg=PA481|archive-date=2016-04-19}} Note: Shawwal 8AH is January 630AD</ref> Muhammad ordered his followers to attack enemies who fled from the [[Battle of Hunayn]] and sought refuge in the fortress of Taif.<ref name="William Muir p. 142">{{cite book |first=William |last=Muir |title=The life of Mahomet and history of Islam to the era of the Hegira |volume=4 |page=142}}</ref>

===Islamic world===
{{Further|Caravanserai|Kasbah|Ribat|Qalat (fortress)}}

===Africa===
The entire city of [[Kerma]] in [[Nubia]] (present day Sudan) was encompassed by fortified walls surrounded by a ditch. Archeology has revealed various Bronze Age bastions and foundations constructed of stone together with either baked or unfired brick.<ref>{{cite book| last = Bianchi| first = Robert Steven| title = Daily Life of the Nubians| year = 2004| publisher = Greenwood Publishing Group| isbn = 978-0-313-32501-4| page = 83 }}</ref>

The [[walls of Benin]] are described as the world's second longest man-made structure, as well as the most extensive earthwork in the world, by the ''Guinness Book of Records, 1974''.<ref>{{cite book |first1=Henry Louis |last1=Gates |first2=Anthony |last2=Appiah |title=Africana: The Encyclopedia of the African and African American Experience |publisher=Basic Civitas Books |date=1999 |page=97 |isbn=0195170555}}</ref><ref>Osadolor, pp. 6–294</ref> The walls may have been constructed between the thirteenth and mid-fifteenth century CE<ref name="Ogundiran">{{cite journal |last1=Ogundiran |first1=Akinwumi |title=Four Millennia of Cultural History in Nigeria (ca. 2000 B.C.–A.D. 1900): Archaeological Perspectives |journal=Journal of World Prehistory |date=June 2005 |volume=19 |issue=2 |pages=133–168|doi=10.1007/s10963-006-9003-y |s2cid=144422848 }}</ref> or, during the first millennium CE.<ref name="Ogundiran"/><ref name="MacEachern">{{cite journal |last1=MacEachern |first1=Scott |title=Two thousand years of West African history |url=https://www.academia.edu/831918 |journal=African Archaeology: A Critical Introduction |date=January 2005 |publisher=Academia}}</ref> Strong citadels were also built other in areas of Africa. [[History of the Yoruba people|Yorubaland]] for example had several sites surrounded by the full range of earthworks and ramparts seen elsewhere, and sited on ground. This improved defensive potential—such as hills and ridges. Yoruba fortifications were often protected with a double wall of trenches and ramparts, and in the Congo forests concealed [[Ditch (fortification)|ditches]] and paths, along with the main works, often bristled with rows of sharpened stakes. Inner defenses were laid out to blunt an enemy penetration with a maze of defensive walls allowing for entrapment and [[crossfire]] on opposing forces.<ref name="Robert July p. 11-39">July, pp. 11–39</ref>

A military tactic of the [[Ashanti Empire|Ashanti]] was to create powerful log [[stockade]]s at key points. This was employed in later wars against the [[British Empire|British]] to block British advances. Some of these fortifications were over a hundred yards long, with heavy parallel tree trunks. They were impervious to destruction by artillery fire. Behind these stockades, numerous Ashanti soldiers were mobilized to check enemy movement. While formidable in construction, many of these strongpoints failed because Ashanti guns, gunpowder and bullets were poor, and provided little sustained killing power in defense. Time and time again British troops overcame or bypassed the stockades by mounting old-fashioned bayonet charges, after laying down some covering fire.<ref>The Ashanti campaign of 1900, (1908) By Sir Cecil Hamilton Armitage, Arthur Forbes Montanaro, (1901) Sands and Co. pp. 130–131</ref>

Defensive works were of importance in the tropical African Kingdoms. In the [[Kingdom of Kongo]] field fortifications were characterized by trenches and low earthen embankments. Such strongpoints ironically, sometimes held up much better against European cannon than taller, more imposing structures.<ref name="Thornton, op. cit">Thornton, pp. 22–39</ref>

===Medieval Europe===
{{Main|Medieval fortification}}
{{See also|Austrian walled towns}}
[[File:Mury obronne Szprotawa.jpg|thumb|Medieval defensive walls and towers in [[Szprotawa]], Poland, made of field stone and [[bog iron]].]]

[[Castra|Roman forts]] and [[hill fort]]s were the main antecedents of [[castle]]s in [[Europe]], which emerged in the 9th century in the [[Carolingian Empire]]. The [[Early Middle Ages]] saw the creation of some towns built around castles. These cities were only rarely protected by simple stone walls and more usually by a combination of both walls and [[Ditch (fortification)|ditches]]. From the 12th century, hundreds of settlements of all sizes were founded all across Europe, which very often obtained the right of fortification soon afterward.       

[[File:John Smith 1624 map of Bermuda with Forts 01.jpg|thumb|[[John Smith (explorer)|John Smith]]'s 1624 map of [[Bermuda]] with the first stone fortifications built by [[England]] in the [[New World]].]]

The founding of urban centers was an important means of territorial expansion and many cities, especially in [[eastern Europe]], were founded precisely for this purpose during the period of [[Ostsiedlung]]. These cities are easy to recognize due to their regular layout and large market spaces. The fortifications of these settlements were continuously improved to reflect the current level of military development. During the [[Renaissance era]], the [[Republic of Venice|Venetian Republic]] raised great walls around cities, and the finest examples, among others, are in [[Nicosia]] (Cyprus), [[Rocca di Manerba del Garda]] (Lombardy), and [[Palmanova]] (Italy), or [[Dubrovnik]] (Croatia), which proved to be futile against attacks but still stand to this day. Unlike the Venetians, the [[Ottoman architecture|Ottomans]] used to build smaller fortifications but in greater numbers, and only rarely fortified entire settlements such as [[Počitelj]], [[Walled city of Vratnik|Vratnik]], and [[Walled city of Jajce|Jajce]] in [[Ottoman Bosnia|Bosnia]].

===Development after introduction of firearms===
{{See also|Venetian Works of Defence between the 16th and 17th centuries: Stato da Terra – Western Stato da Mar}}

Medieval-style fortifications were largely made obsolete by the arrival of [[cannon]]s on the 14th century [[battle]]field. Fortifications in the age of [[black powder]] evolved into much lower structures with greater use of [[Ditch (fortification)|ditches]] and [[earthworks (engineering)|earth]] [[Rampart (fortification)|ramparts]] that would absorb and disperse the energy of cannon fire. Walls exposed to direct cannon fire were very vulnerable, so were sunk into ditches fronted by earth slopes.

This placed a heavy emphasis on the [[geometry]] of the fortification to allow defensive cannonry interlocking fields of fire to cover all approaches to the lower and thus more vulnerable walls.

[[File:Table of Fortification, Cyclopaedia, Volume 1.jpg|thumb|upright|Table of a typical [[bastion fort]], 1728. The development of bastion forts resulted from the increased use of cannons and firearms in the 14th century.]]

The evolution of this new style of fortification can be seen in transitional forts such as Sarzanello<ref>Harris, J., [http://www.fsgfort.com/FortArt/Fort37Art1.htm "Sarzana and Sarzanello – Transitional Design and Renaissance Designers"] {{webarchive|url=https://web.archive.org/web/20110726181015/http://www.fsgfort.com/FortArt/Fort37Art1.htm |date=2011-07-26 }}, ''Fort'' ([[Fortress Study Group]]), No. 37, 2009, pp. 50–78</ref> in North West Italy which was built between 1492 and 1502. Sarzanello consists of both crenellated walls with towers typical of the medieval period but also has a [[ravelin]] like angular gun platform screening one of the curtain walls which is protected from flanking fire from the towers of the main part of the fort. Another example is the [[fortifications of Rhodes]] which were ''frozen'' in 1522 so that Rhodes is the only European walled town that still shows the transition between the classical medieval fortification and the modern ones.<ref name="restoration">{{Cite book | title = Medieval Town of Rhodes – Restoration Works (1985–2000) – Part One | publisher = Ministry of Culture – Works supervision committee for the monuments of the medieval town of Rhodes | year = 2001 | place = Rhodes}}</ref> A manual about the construction of fortification was published by [[Giovanni Battista Zanchi]] in 1554.

Fortifications also extended in depth, with protected batteries for defensive cannonry, to allow them to engage attacking cannons to keep them at a distance and prevent them from bearing directly on the vulnerable walls.

[[File:Suomenlinna.jpg|thumb|[[Suomenlinna]], a [[sea fortress]] from 18th century in [[Helsinki]], Finland]]

The result was [[Star fort|star shaped fortifications]] with tier upon tier of hornworks and [[bastion]]s, of which [[Fort Bourtange]] is an excellent example. There are also extensive fortifications from this era in the [[Northern Europe|Nordic]] states and in [[Great Britain|Britain]], the fortifications of [[Berwick-upon-Tweed]] and the harbor [[archipelago]] of [[Suomenlinna]] at [[Helsinki]] being fine examples.

===19th century===
During the 18th century, it was found that the continuous [[enceinte]], or main defensive enclosure of a bastion fortress, could not be made large enough to accommodate the enormous field armies which were increasingly being employed in Europe; neither could the defenses be constructed far enough away from the fortress town to protect the inhabitants from bombardment by the besiegers, the range of whose guns was steadily increasing as better manufactured weapons were introduced. Therefore, since refortifying the [[Prussia]]n fortress cities of [[Koblenz]] and [[Köln]] after 1815, the principle of the '''ring fortress''' or '''girdle fortress''' was used: forts, each several hundred meters out from the original enceinte, were carefully sited so as to make best use of the terrain and to be capable of mutual support with neighboring forts.<ref>[https://prussia.online/Data/Book/th/the-forts-and-fortifications-of-europe-1815-1945/Kaufmann%20J.,%20Kaufmann%20H.%20The%20Forts%20and%20Fortifications%20of%20Europe,%201815-1945%20(2014),%20OCR.pdf The Forts and Fortifications of Europe 1815-1945]</ref> Gone were citadels surrounding towns: forts were to be moved some distance away from cities to keep the enemy at a distance so their artillery could not bombard said urbanized settlements. From now on a ring of forts were to be built at a spacing that would allow them to effectively cover the intervals between them.

The arrival of [[explosive shell]]s in the 19th century led to yet another stage in the evolution of fortification. [[Star fort]]s did not fare well against the effects of high explosives and the intricate arrangements of bastions, flanking batteries and the carefully constructed lines of fire for the defending cannon could be rapidly disrupted by explosive shells.

[[File:Malta Delimara one.jpg|thumb|left|The ditch and [[counterscarp]] of [[Fort Delimara]]. Built in 1878, Delimara was built as a typical [[polygonal fort]] ditches and counterscarps made to be very deep, vertically sided, and cut directly into the rocks.]]

Worse, the large open ditches surrounding forts of this type were an integral part of the defensive scheme, as was the covered way at the edge of the [[counterscarp]]. The ditch was extremely vulnerable to bombardment with explosive shells.

In response, military engineers evolved the [[Polygonal fort|polygonal]] style of fortification. The ditch became deep and vertically sided, cut directly into the native rock or soil, laid out as a series of straight lines creating the central fortified area that gives this style of fortification its name.

Wide enough to be an impassable barrier for attacking troops but narrow enough to be a difficult target for enemy shellfire, the ditch was swept by fire from defensive [[blockhouses]] set in the ditch as well as firing positions cut into the outer face of the ditch itself.

The profile of the fort became very low indeed, surrounded outside the ditch covered by [[caponiers]] by a gently sloping open area so as to eliminate possible cover for enemy forces, while the fort itself provided a minimal target for enemy fire. The entrypoint became a sunken gatehouse in the inner face of the ditch, reached by a curving ramp that gave access to the gate via a rolling bridge that could be withdrawn into the gatehouse.

[[File:14-46-35-f-mutzig.jpg|thumb|The tunnels of [[Fort de Mutzig]], German fortifications built in 1893. By the 19th century, tunnels were used to connect [[blockhouse]]s and firing points in the ditch to the fort.]]

Much of the fort moved underground. Deep passages and [[tunnel network]]s now connected the [[blockhouse]]s and firing points in the ditch to the fort proper, with [[magazine (artillery)|magazines]] and machine rooms deep under the surface. The guns, however, were often mounted in open emplacements and protected only by a [[parapet]]; both in order to keep a lower profile and also because experience with guns in closed [[casemate]]s had seen them put out of action by rubble as their own casemates were collapsed around them.

The new forts abandoned the principle of the bastion, which had also been made obsolete by advances in arms. The outline was a much-simplified polygon, surrounded by a ditch. These forts, built in masonry and shaped stone, were designed to shelter their garrison against bombardment. One organizing feature of the new system involved the construction of two defensive curtains: an outer line of forts, backed by an inner ring or line at critical points of terrain or junctions (see, for example, [[Séré de Rivières system]] in France).

Traditional fortification however continued to be applied by European armies engaged in warfare in colonies established in Africa against lightly armed attackers from amongst the indigenous population. A relatively small number of defenders in a fort impervious to primitive weaponry could hold out against high odds, the only constraint being the supply of ammunition.

===20th and 21st centuries===
[[File:Fort Campbell 09.jpg|thumb|Gun emplacement in [[Fort Campbell (Malta)|Fort Campbell]], built in the 1930s. Due to the threat of [[aerial warfare]], the buildings were placed at a distance from each other, making it difficult to find from the air.]]

[[Steel]]-and-[[concrete]] fortifications were common during the 19th and early 20th centuries. However, the advances in modern warfare since [[World War I]] have made large-scale fortifications [[obsolete]] in most situations. In the 1930s and 1940s, some fortifications were built with designs taking into consideration the new threat of [[aerial warfare]], such as [[Fort Campbell (Malta)|Fort Campbell]] in Malta.<ref>{{cite web|last1=Mifsud|first1=Simon|title=Fort Campbell|url=http://www.militaryarchitecture.com/index.php/Fortifications/fort-campbell.html|website=MilitaryArchitecture.com|access-date=15 March 2015|date=14 September 2012|url-status=live|archive-url=https://web.archive.org/web/20151115113234/http://www.militaryarchitecture.com/index.php/Fortifications/fort-campbell.html|archive-date=15 November 2015}}</ref> Despite this, only underground [[bunker]]s are still able to provide some protection in modern wars. Many historical fortifications were demolished during the modern age, but a considerable number survive as popular tourist destinations and prominent local [[landmark]]s today.

The downfall of permanent fortifications had two causes:
* The ever-escalating power, speed, and reach of artillery and airpower meant that almost any target that could be located could be destroyed if sufficient force were massed against it. As such, the more resources a defender devoted to reinforcing a fortification, the more combat power that fortification justified being devoted to destroying it, if the fortification's destruction was demanded by an attacker's strategy. From [[World War II]], [[bunker buster]]s were used against fortifications. By 1950, [[nuclear weapon]]s were capable of destroying entire cities and producing dangerous [[radiation]]. This led to the creation of civilian nuclear [[air raid shelter]]s.
* The second weakness of permanent fortification was its very permanency. Because of this, it was often easier to go around a fortification and, with the rise of mobile warfare in the beginning of World War II, this became a viable offensive choice. When a defensive line was too extensive to be entirely bypassed, massive offensive might could be massed against one part of the line allowing a breakthrough, after which the rest of the line could be bypassed. Such was the fate of the many defensive lines built before and during World War II, such as the [[Siegfried Line]], the [[Stalin Line]], and the [[Atlantic Wall]]. This was not the case with the [[Maginot Line]]; it was designed to force the Germans to invade other countries (Belgium or Switzerland) to go around it, and was successful in that sense.<ref>{{cite book |last=Halter |first=Marc |title=History of the Maginot Line |publisher=Moselle River |date=2011 |isbn=978-2-9523092-5-7}}{{page needed|date=August 2022}}</ref>
[[File:Image-GBU-24 Missile testmontage-gi BLU-109 bomb.jpg|thumb|left|upright|A [[GBU-24 Paveway III|GBU-24]] {{cvt|2000|lb}} bomb hits the ground. The development of [[bunker buster]]s, bombs designed to penetrate hardened targets buried underground, led to a decline in the use of fortifications.]]
Instead field fortification rose to dominate defensive action. Unlike the [[trench warfare]] which dominated World War I, these defenses were more temporary in nature. This was an advantage because since it was less extensive it formed a less obvious target for enemy force to be directed against.

If sufficient power were massed against one point to penetrate it, the forces based there could be withdrawn and the line could be reestablished relatively quickly. Instead of a supposedly impenetrable defensive line, such fortifications emphasized [[defense in depth]], so that as defenders were forced to pull back or were overrun, the lines of defenders behind them could take over the defense.

Because the mobile offensives practiced by both sides usually focused on avoiding the strongest points of a [[defensive line]], these defenses were usually relatively thin and spread along the length of a line. The defense was usually not equally strong throughout, however.

The strength of the defensive line in an area varied according to how rapidly an attacking force could progress in the terrain that was being defended—both the terrain the defensive line was built on and the ground behind it that an attacker might hope to break out into. This was both for reasons of the strategic value of the ground, and its defensive value.

This was possible because while offensive tactics were focused on mobility, so were defensive tactics. The dug-in defenses consisted primarily of infantry and [[antitank gun]]s. Defending [[tank]]s and [[tank destroyer]]s would be concentrated in mobile [[brigade]]s behind the defensive line. If a major offensive was launched against a point in the line, mobile reinforcements would be sent to reinforce that part of the line that was in danger of failing.

Thus the defensive line could be relatively thin because the bulk of the fighting power of the defenders was not concentrated in the line itself but rather in the mobile reserves. A notable exception to this rule was seen in the defensive lines at the [[Battle of Kursk]] during World War II, where German forces deliberately attacked the strongest part of the [[Soviet Union|Soviet]] defenses, seeking to crush them utterly.

The [[terrain]] that was being defended was of primary importance because [[open terrain]] that tanks could move over quickly made possible rapid advances into the defenders' rear areas that were very dangerous to the defenders. Thus such terrain had to be defended at all costs.

[[File:NORADNorth-Portal.jpg|thumb|[[Cheyenne Mountain Complex]] is an underground [[bunker]] used by [[North American Aerospace Defense Command]]. Cheyenne Mountain is an example of a mid-20th century fortification built deep in a mountain.]]

In addition, since in theory the defensive line only had to hold out long enough for mobile reserves to reinforce it, terrain that did not permit rapid advance could be held more weakly because the enemy's advance into it would be slower, giving the defenders more time to reinforce that point in the line. For example, the [[Battle of the Hurtgen Forest]] in Germany during the closing stages of World War II is an excellent example of how difficult terrain could be used to the defenders' advantage.

After World War II, [[intercontinental ballistic missile]]s capable of reaching much of the way around the world were developed, so speed became an essential characteristic of the strongest militaries and defenses. [[Missile silo]]s were developed, so missiles could be fired from the middle of a country and hit cities and targets in another country, and airplanes (and [[aircraft carrier]]s) became major defenses and offensive weapons (leading to an expansion of the use of airports and airstrips as fortifications). Mobile defenses could be had underwater, too, in the form of [[ballistic missile submarine]]s capable of firing [[submarine launched ballistic missile]]s. Some bunkers in the mid to late 20th century came to be buried deep inside mountains and prominent rocks, such as [[Gibraltar]] and the [[Cheyenne Mountain Complex]]. On the ground itself, [[minefield]]s have been used as hidden defenses in modern warfare, often remaining long after the wars that produced them have ended.

[[Demilitarized zone]]s along borders are arguably another type of fortification, although a passive kind, providing a buffer between potentially hostile militaries.

===Military airfields===
[[Military airfield]]s offer a fixed "target rich" environment for even relatively small enemy forces, using [[hit-and-run tactics]] by ground forces, stand-off attacks (mortars and rockets), air attacks, or ballistic missiles. Key targets—aircraft, munitions, fuel, and vital technical personnel—can be protected by fortifications.

Aircraft can be protected by [[Revetment (aircraft)|revetment]]s, [[hesco barrier]]s, [[hardened aircraft shelter]]s and [[underground hangar]]s which will protect from many types of attack. Larger aircraft types tend to be based outside the operational theater.

Munition storage follows safety rules which use fortifications (bunkers and bunds) to provide protection against accident and chain reactions (sympathetic detonations). Weapons for rearming aircraft can be stored in small fortified ''expense'' stores closer to the aircraft. At Biên Hòa, South Vietnam, on the morning of May 16, 1965, as aircraft were being refueled and armed, a chain reaction explosion destroyed 13 aircraft, killed 34 personnel, and injured over 100; this, along with damage and losses of aircraft to enemy attack (by both [[Infiltration tactics|infiltration]] and stand-off attacks), led to the construction of revetments and shelters to protect aircraft throughout [[South Vietnam]].

Aircrew and ground personnel will need protection during enemy attacks and fortifications range from culvert section "duck and cover" shelters to permanent air raid shelters. Soft locations with high personnel densities such as accommodation and messing facilities can have limited protection by placing prefabricated concrete walls or barriers around them, examples of barriers are [[Jersey Barrier]]s, T Barriers or Splinter Protection Units (SPUs). Older fortification may prove useful such as the old 'Yugo' pyramid shelters built in the 1980s which were used by US personnel on 8 Jan 2020 when Iran fired 11 ballistic missiles at [[Al Asad Airbase|Ayn al-Asad Airbase]] in Iraq.

Fuel is volatile and has to comply with rules for storage which provide protection against accidents. Fuel in underground bulk fuel installations is well protected though valves and controls are vulnerable to enemy action. Above-ground tanks can be susceptible to attack.

Ground support equipment will need to be protected by fortifications to be usable after an enemy attack.

Permanent (concrete) guard fortifications are safer, stronger, last longer and are more cost-effective than [[sandbag]] fortifications. Prefabricated positions can be made from concrete culvert sections. The British Yarnold Bunker is made from sections of a concrete pipe.

Guard towers provide an increased field of view but a lower level of protection.

Dispersal and camouflage of assets can supplement fortifications against some forms of airfield attack.

====Counterinsurgency====
Just as in colonial periods, comparatively obsolete fortifications are still used for low intensity conflicts. Such fortifications range in size from small patrol bases or [[forward operating base]]s up to huge [[airbase]]s such as [[Camp Bastion]]/[[Camp Leatherneck|Leatherneck]] in [[Afghanistan]]. Much like in the 18th and 19th century, because the enemy is not a powerful military force with the heavy weaponry required to destroy fortifications, walls of [[gabion]], [[sandbag]] or even simple mud can provide protection against small arms and antitank weapons—although such fortifications are still vulnerable to mortar and artillery fire.

==Forts==
[[File:Fortaleza Ozama RD 11 2017 6495.jpg|thumb|The [[Fortaleza Ozama|Ozama Fortress]] in [[Santo Domingo]], Dominican Republic is recognized by UNESCO for being the oldest military construction of European origin in the Americas.<ref>{{cite web|url=https://whc.unesco.org/en/list/526|title=Colonial City of Santo Domingo. Outstanding Universal Value|website=UNESCO World Heritage Centre website}}</ref>]]

Forts in modern American usage often refer to space set aside by governments for a permanent military facility; these often do not have any actual fortifications, and can have specializations (military barracks, administration, medical facilities, or intelligence).

However, there are some modern fortifications that are referred to as forts. These are typically small semipermanent fortifications. In urban combat, they are built by upgrading existing structures such as houses or public buildings. In field warfare they are often log, sandbag or [[gabion]] type construction.

Such forts are typically only used in low-level conflicts, such as counterinsurgency conflicts or very low-level conventional conflicts, such as the [[Indonesia–Malaysia confrontation]], which saw the use of log forts for use by forward [[platoon]]s and [[Company (military unit)|companies]]. The reason for this is that static above-ground forts cannot survive modern direct or indirect fire weapons larger than mortars, RPGs and small arms.

==Prisons and others==
Fortifications designed to keep the inhabitants of a facility in rather than attacker out can also be found, in [[prisons]], [[concentration camps]], and other such facilities. Those are covered in other articles, as most prisons and concentration camps are not primarily military forts (although forts, camps, and garrison towns have been used as prisons and/or concentration camps; such as [[Theresienstadt]], [[Guantanamo Bay detention camp]] and the [[Tower of London]] for example). 

==Field fortifications==
{{Main|Trench warfare}}

==Notes==
{{Reflist}}

==References==
* {{EB1911|wstitle=Fortification and Siegecraft|volume=10|pages=679–725|first=Louis Charles|last=Jackson}}

==Bibliography==
* July, Robert ''Pre-Colonial Africa'', Charles Scribner, 1975.
* Murray, Nicholas. "The Development of Fortifications", ''The Encyclopedia of War'', Gordon Martel (ed.). WileyBlackwell, 2011.
* Murray, Nicholas. ''The Rocky Road to the Great War: The Evolution of Trench Warfare to 1914''. Potomac Books Inc. (an imprint of the University of Nebraska Press), 2013.
* Osadolor, Osarhieme Benson, "The Military System of Benin Kingdom 1440–1897", (UD), Hamburg University: 2001 [https://ediss.sub.uni-hamburg.de/volltexte/2001/544/pdf/Disse.pdf copy].
* Thornton, John Kelly ''Warfare in Atlantic Africa'', 1500–1800, Routledge: 1999, {{ISBN|1857283937}}.

==External links==
{{Wiktionary}}
{{Commons}}
* [http://www.fsgfort.com Fortress Study Group]
* {{webarchive|url=https://web.archive.org/web/20181205190113/http://www.militaryarchitecture.com|date=5 December 2018|title=Military Architecture}}
* [http://www.icofort.org ICOFORT]

{{Fortifications}}
{{Stonemasonry}}
{{Authority control}}
{{Military and war}}

[[Category:Fortifications| ]]
[[Category:Engineering barrages]]
[[Category:Military strategy]]
[[Category:Military installations]]
[[Category:Forts]]