Trajan’s Bridge, first bridge spanning the Danube River, built east of the Iron Gate Rapids at Turnu Severin by the Roman emperor Trajan (reigned 98–117 ce) to guarantee the supply line of his legions in conquered Dacia. The engineer, probably Trajan’s lieutenant, Apollodorus of Damascus, used timber arches mounted on masonry piers to span the 800-metre- (0.5-mile-) wide river. A century and a half later the emperor Aurelian withdrew from Dacia and demolished the bridge, which is memorialized on Trajan’s Column in Rome. Its 52-metre (170-foot) spans were the longest built for more than a thousand years.