Trajan, (53?–117), a Roman emperor. The second of the so-called Five Good Emperors, he shunned the tyrannical practices common among his predecessors and restored the senate's authority. Trajan had numerous roads, aqueducts, and other public facilities built. He led the Roman army in many campaigns of conquest; during his reign the empire reached its greatest size. His expenditures were so vast, however, that prosperity could be maintained only by debasing the currency.

Trajan's full name was Marcus Ulpius Trajanus (or Traianus). He was born in Spain, the son of a Roman general, and made the army his career. In 97 he was adopted as successor by the emperor Nerva, whom he succeeded a few months later while in Germany. Upon concluding his campaign there in 99 Trajan returned to Rome. Two years later he marched against Dacia (Romania), which was added to the empire in 106. The Column of Trajan in the Forum of Trajan in Rome was erected to commemorate this victory.

About 113 the senate gave Trajan the title of Optimus (the best), and soon afterward he led his army against the Parthian Empire, in western Asia. Armenia, Assyria, and Mesopotamia were conquered. Taken fatally ill in the field, Trajan died in Cilicia. On his deathbed he adopted as successor his cousin Hadrian.