Trajan's Bridge (Romanian: Podul lui Traian; Serbian: Трајанов мост, Trajanov Most) or Bridge of Apollodorus over the Danube was a Roman segmental arch bridge, the first to be built over the lower Danube. Though it lasted less than 200 years before being destroyed, for more than 1,000 years, it was the longest arch bridge in both total and span length.

The bridge was constructed by the Greek architect Apollodorus of Damascus for the deployment of Roman troops in the war against Dacia, in 105 AD.

The bridge was situated East of the Iron Gates, near the 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.

The structure was 1,135 m (3,724 ft) in length (the Danube is 800 m (2,600 ft) wide in that area), 15 m (49 ft) in width, and 19 m (62 ft) in height (measured from the river's surface). At each end was a Roman castrum, each built around an entrance (crossing was possible only by walking through the camp).

Trajan ( /ˈtreɪdʒən/; Latin: Marcus Ulpius Nerva Traianus Augustus; 18 September 53 – 9 August 117), was Roman Emperor from 98 to 117 AD. Born into a non-patrician family in the province of Hispania Baetica, Trajan rose to prominence during the reign of emperor Domitian. Serving as a legatus legionis in Hispania Tarraconensis, in 89 Trajan supported the emperor against a revolt on the Rhine led by Antonius Saturninus.

In September 96, Domitian was succeeded by Marcus Cocceius Nerva, an old and childless senator who proved to be unpopular with the army. After a brief and tumultuous year in power, a revolt by members of the Praetorian Guard compelled him to adopt the more popular Trajan as his heir and successor. Nerva died on 27 January 98, and was succeeded by his adopted son without incident.

As a civilian administrator, Trajan is best known for his extensive public building program which reshaped the city of Rome and left multiple enduring landmarks such as Trajan's Forum, Trajan's Market and Trajan's Column. Early in his reign, he annexed the Nabataean kingdom, creating the province of Arabia Petraea. His conquest of Dacia enriched the empire greatly — the new province possessed many valuable gold mines.