Image from TravelBiz Blog
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.
Image from Wikipedia
The structure was 1,135 m in length (the Danube is 800 meters-wide in that area), 15 m in width, and reached 19 m 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).
Image from Realitatea Dunăreană
Its engineer, Apollodorus of Damascus, used wooden arches set on twenty masonry pillars (made with bricks, mortar and pozzolana cement) that spanned 38 m 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.
Image from Dummidumbwit's Weblog
The bridge was destroyed by Aurelian (270-275), 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.
Image from Structurae
In 1979, Trajan's Bridge was added to the Monument of Culture of Exceptional Importance, and in 1983 on Archaeological Sites of Exceptional Importance list.
Apollodorus of Damascus was a Greek engineer, architect, designer and sculptor who flourished during the 2nd century AD, from Damascus, Roman Syria. He was a favorite of Trajan, for whom he constructed Trajan's Bridge over the Danube for the 105-106 campaign in Dacia. He also designed the Forum Trajanum and Trajan's Column within the city of Rome, beside several smaller projects. Apollodorus also designed the triumphal arches of Trajan at Beneventum and Ancona. He is also widely credited as the architect of the Pantheon, and cited as the builder of the Alconétar Bridge in Spain. In 106 he also completed or restored the odeon begun in the Campus Martius under Domitian.