Hadrian, or Adrian, both (76–138 A.D.), Roman emperor from 117 to 138. His full name was Publius Aelius Hadrianus. Rome prospered under Hadrian, an able soldier and conscientious administrator. He visited each province of the empire at least once to acquaint himself with local conditions and he commissioned a jurist to classify Roman laws systematically.

Hadrian, born in Spain of Italian descent, was a cousin of Trajan, emperor from 98 to 117. Hadrian became an army officer and was twice consul before succeeding his cousin. He made the Euphrates River the eastern boundary of the empire, abandoning previous conquests by Trajan. He ordered the construction of a wall in northern England to keep out the warlike Caledonians from Scotland. This structure, called Hadrian's Wall, was completed in 128.

Hadrian was an enthusiastic builder. In Rome he had a huge mausoleum (now called Castel Sant'Angelo) built for himself and had the Pantheon erected on the site of an earlier temple. His villa, built on a plain near Tivoli, was one of the largest and most elaborate country estates of ancient Rome. He had Athens extensively reconstructed, and near Byzantium he founded the city of Hadrianopolis, or Andrianople (later called Edirne). After putting down a Jewish rebellion in Palestine (132–35) Hadrian built on the ruins of Jerusalem a new city, from which Jews were excluded.