Trajan's Bridge was the first bridge built on the lower Danube river, east from the Iron Gates, near what is now the city of Drobeta-Turnu Severin, Romania. The bridge was built to provide supplies for the Roman legions that were fighting in Dacia.

The Danube is 800 meters wide at the location of the bridge. The bridge extended past the river banks for a total length of 1135 meters. It was 15 meters wide and 19 meters above the water. Each end of the bridge was guarded by a Roman castrum: crossing could be made only by walking through the castrum.

The engineer, Apollodorus of Damascus, used wooden arches set on twenty masonry pillars (made with bricks, mortar and pozzolana cement) that spanned 52-meters each. However, the way it was built — in such a short time (103-105) — is still a mystery and it is thought that the course of the Danube may have been diverted during the construction.

A memorial plaque that commemorates Trajan's victory against the Dacians is located on the Serbian side facing Romania.

The bridge was destroyed by Aurelian, after the Roman Empire withdrew its troops from Dacia. It was for more than a thousand years the longest bridge that had ever been built.

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, as probably four were swept away by water in the meantime. Nowadays, only the first pillars can be seen on the banks of the Danube.