Trajan's Bridge (Romanian: Podul lui Traian; Serbian: Трајанов мост, Trajanov Most) or Bridge of Apollodorus over the Danube was a Roman bridge , the first to be built over the lower Danube. For more than a thousand years, it was the longest arch bridge in the world to have been built, in terms of both total and span length. The bridge was constructed by the Greek architect Apollodorus of Damascus.
The bridge was situated east from the Iron Gates, nearby the present-day cities of Drobeta-Turnu Severin (Romania) and Kladovo (Serbia). Its construction was ordered by Emperor Trajan as a supply route for the Roman legions fighting in Dacia (see Trajan's Dacian Wars).
The structure was 1,135 meters in length (the Danube is 800 meters-wide in that area), 15 meters in width, and reached 19 meters in height (measured from the river's surface). At each end was situated a Roman castrum, each of them built around an entrance (crossing was possible only by walking through the camp).
Its engineer, Apollodorus of Damascus, used wooden arches set on twenty masonry pillars (made with bricks, mortar and pozzolana cement) that spanned 38-meters each . Nevertheless, it was built over an unusually short period of time (between 103 and 105) — one possible explanation is that the river was diverted during the bridge's construction.
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A Roman memorial plaque ("Tabula Traiana"), 4 meters in width and 1.75 meters in height, commemorating the completion of Trajan's military road is located on the Serbian side facing Romania near Ogradina. It reads:
IMP. CAESAR. DIVI. NERVAE. FThe text was interpreted by Otto Benndorf to mean:
The bridge was destroyed by Aurelian, after the Roman Empire withdrew its troops from Dacia.
The twenty pillars could still be seen in the year 1856, when the level of the Danube hit a record low. In 1906, the International Commission of the Danube decided to destroy two of the pillars that were obstructing navigation.
In 1932, there were 16 remaining pillars underwater, but in 1982 only 12 were mapped by archeologists — the other four had probably been swept away by water. Only the entrance pillars are nowadays visible on either bank of the Danube.