Editing Fortification (section)

===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.