The Roman emperor Hadrian (76-138), or Publius Aelius Hadrianus, reversed the expansionist policies of Rome in a permanent shift to the defensive.

Hadrian was born in Rome on Jan. 24, 76. A ward of his uncle, Emperor Trajan, he spent the first 30 years of his life as a general and public official under Trajan's tutelage. There was a cloud over Hadrian's accession, for Trajan, though a relation, did not adopt him until on his deathbed, and there was some doubt even of that. The prompt execution of four possible rivals, though done without Hadrian's knowledge, also raised doubt.

At Hadrian's accession the Jewish revolt over much of the East and Trajan's faltering Parthian War were his first concerns. He ended the war by abandoning Armenia and Trajan's Parthian conquests, quelled the Jewish revolt, and returned to Rome (118). His administration was marked throughout by great care for finances—Trajan's wars had proved too costly—and strict governmental supervision of an increasing number of sectors of public and private life. Of great importance was his policy of appointing equestrians (knights), the class below the senators, instead of
freedmen to head the imperial bureaus. He thus recognized that these bureaus were organs of state, not household chores to be left to the Emperor's personal servants.

Hadrian's defensive policy posed problems of military discipline and morale, since it is always harder to maintain the efficiency of an army whose training may never be put to use. His answer was endless personal supervision, and he spent approximately half his reign touring the provinces on inspection. The system worked under Hadrian, but in time the efficiency of the armies declined.

Another result of Hadrian's defensive policy was the need for clearly marked frontiers and for border fortresses. He strengthened the defenses, notably in Germany and in Britain, where the most famous of all his frontier works, Hadrian's Wall, crosses Britain approximately along the border between England and Scotland