On March 5, AD 363, the emperor Julian marched out of Antioch at the head of 80,000 battle-tested Roman soldiers for his rendezvous with destiny. Known to history as "The Apostate", Julian had become emperor two years before while serving as caesar in the west under Constantinus II. There he had made a reputation for himself as a competent military commander, defeating the Alemanni a series of battles and restoring order to the Rhine frontier.
His success won him the acclaim of his troops, who declared him Augustus in AD 360. This act sparked a civil war between Julian and Constantius, but the latter died while on the march to engage Julian. As a result, Julian became the sole ruler of the empire.
Though a nephew of Constantine the Great, Julian rejected the Christian faith of his uncle and embraced philosophic paganism with an evangelical fervor. As emperor, he sought to undermine the favored status that the Church had enjoyed within the empire. He called Christ, "the Galilean" and referred to Christian churches as "charnel houses". To prove Christ a false prophet, he commenced re-construction of the Temple in Jerusalem--an effort that came to a stunning end when the works were destroyed by an earthquake.
Continuing strife on the eastern frontier forced Julian to take military action against the Persians in AD 363. After an extended and tumultuous stay in Antioch, Julian departed with his soldiers for what would be the final campaign of his career.
Though initially successful, Julian's forces were eventually worn down by hunger and constant attack while deep within Persian territory. During an ambush, Julian was struck by a javelin and mortally wounded. Before he died, he supposedly uttered the phrase, "Thou hast conquered, Galilean."
Wikipedia's entry on Julian is generally fair.
The entry on Julian in the Catholic Encyclopedia is also noteworthy.