The Roman emperor Julian (331-363), or Flavius Claudius Julianus, tried to turn the Roman world from Christianity to a reformed paganism and thus earned the sobriquet "the Apostate."

Julian was born at Constantinople, the son of Julius Constantius, half brother of Constantine the Great. When Constantine died in 337, nearly all his relatives except his three sons were killed, and Julian and his half brother Constantius Gallus were spared because of their extreme youth. The boys were confined to a castle in Cappadocia, where they lived until 351, and were given a monkish education. Julian idealized the ancient Hellenic world and was attracted by Greek literature and philosophy; he despised what he considered the falsity and hypocrisy of Christianity.

By 351 Constantius II was Constantine's sole surviving son, and he brought Gallus out of retirement and made him the administrator of the East. Julian remained in retirement, but when Gallus proved...