Editing Trajan's Bridge (section)

==Design and construction==

Apollodorus used wooden arches, each spanning {{convert|38|m|ft|abbr=on}}, set on twenty masonry pillars made of bricks, mortar, and [[pozzolana]] cement.<ref>The earliest identified Roman caisson construction was at Cosa, a small Roman colony north of Rome, where similar caissons formed a breakwater as early as the 2nd century BC: ''International Handbook of Underwater Archaeology'', 2002.</ref><ref>Fernández Troyano, Leonardo, "Bridge Engineering - A Global Perspective", Thomas Telford Publishing, 2003</ref> It was built unusually quickly (between 103 and 105), employing the construction of a wooden [[caisson (engineering)|caisson]] for each pier.<ref>In the first century BC, Roman engineers had employed wooden caissons in constructing the [[Herod the Great|Herodian]] harbour at Caesarea Maritima: Carol V. Ruppe, Jane F. Barstad, eds.  ''International Handbook of Underwater Archaeology'', 2002, "Caesarea" pp505f.</ref>

Apollodorus applied the technique of river flow relocation, using the principles set by [[Thales of Miletus]] some six centuries beforehand. Engineers waited for a low water level to dig a canal, west of the modern downtown of Kladovo. The water was redirected {{convert|2|km|abbr=on}} downstream from the construction site, through the lowland of {{ill|Ključ region|sr|Ključ (oblast)}}, to the location of the modern village of [[Mala Vrbica (Kladovo)|Mala Vrbica]]. Wooden pillars were driven into the river bed in a rectangular layout, which served as the [[Foundation (engineering)|foundation]] for the supporting [[Pier (architecture)|piers]], which were coated with clay. The hollow piers were filled with stones held together by [[Mortar (masonry)|mortar]], while from the outside they were built around with [[Roman bricks]]. The bricks can still be found around the village of Kostol, retaining the same physical properties that they had 2 millennia ago. The piers were {{convert|44.46|m|abbr=on}} tall, {{convert|17.78|m|abbr=on}} wide and {{convert|50.38|m|abbr=on}} apart.<ref name=Politika>{{Citation | author = Ranko Jakovljević | title = Srećniji od Avgusta, bolji of Trajana | newspaper = [[Politika]]-Kulturni dodatak | page = 05 | language = sr | date = 9 September 2017 }}</ref> It is considered today that the bridge construction was assembled on the land and then installed on the pillars. A mitigating circumstance was that the year the relocating canals were dug was very dry and the water level was quite low. The river bed was almost completely drained when the foundation of the pillars began. There were 20 pillars in total in an interval of {{convert|50|m|abbr=on}}. [[Oak]] wood was used and the bridge was high enough to allow ship transport on the Danube.<ref name=magazin/>

The bricks also have a historical value, as the members of the [[Roman legions]] and [[Cohort (military unit)|cohorts]] which participated in the construction of the bridge carved the names of their units into the bricks. Thus, it is known that work was done by the legions of [[Legio IV Flavia Felix|IV Flavia Felix]], [[Legio VII Claudia|VII Claudia]], [[Legio V Macedonica|V Macedonica]] and [[Legio XIII Gemina|XIII Gemina]] and the cohorts of I Cretum, II Hispanorum, III Brittonum and I Antiochensium.<ref name=Politika/>