Hadrian rose through Roman military and administrative offices under Trajan, serving in provincial commands and reaching the consulship in 108 CE. When Trajan died in 117, Hadrian's succession was supported by the imperial household and army. The claim that Trajan had adopted him at the end of his life was disputed in antiquity. Executions of several leading senators damaged relations with the Senate, although Hadrian denied personal responsibility.

He abandoned Trajan's recent conquests beyond the Euphrates and emphasized consolidation over further expansion. Much of his reign was spent traveling through the provinces, inspecting troops, strengthening defenses, and dealing with local administration. His visit to Britain in 122 was followed by construction of Hadrian's Wall, a fortified frontier across northern England.

Hadrian promoted legal and administrative organization. He commissioned the jurist Salvius Julianus to consolidate the praetorian edict, helping make established legal rules more systematic. He took an interest in civic building and local elites, especially in the Greek-speaking east. At Athens he supported monumental projects and the Panhellenion, an association of Greek cities linked to the emperor. In Rome his reign included reconstruction of the Pantheon, while the villa at Tibur combined elaborate architecture, gardens, and references to places encountered across the empire.

The death of his companion Antinous in the Nile in 130 led Hadrian to establish Antinoopolis and support a cult commemorating him. In Judaea the foundation of the Roman colony Aelia Capitolina at Jerusalem and other imperial policies were associated with escalating conflict. The precise relationship between these measures and the outbreak of the Bar Kokhba revolt in 132 is debated. Roman suppression of the revolt by 135 caused enormous destruction and loss of life and imposed severe restrictions on Jewish access to Jerusalem.

Ill health and succession questions dominated Hadrian's final years. His first adopted heir, Aelius Caesar, died before him, and in 138 he adopted Antoninus Pius, requiring him in turn to adopt the future Marcus Aurelius and Lucius Verus. Hadrian died later that year. His career established a model of an emperor engaged directly with provincial government and military frontiers, but the stability and cultural patronage of his reign coexisted with ruthless political measures and the devastation of communities that resisted imperial authority.