Constantius, after dealing with the rebellions of Magnentius and Sylvanus, feels the need for a permanent representative in Gaul.

His twenty-three year-old nephew Julian is in 355 summoned from Greece to appear before the emperor in Mediolanum.

This is a difficult decision for a paranoid ruler who regards all his relatives with intense suspicion and has already put to death two uncles and seven cousins, including Julian's half-brother Constantius Gallus, but Constantius' own family purges had left him little choice: Julian is his sole surviving adult male close relative.

Julian, who has studied at Pergamon, at Ephesus, and lately at Athens, has adopted the cult of Sol Invictus, the Unconquered Sun.

He had arrived at Sirmium “still wearing his student's gown.”

Julian is on November 6 duly proclaimed and invested as Caesar of the West, an honor that he accepts with justifiable foreboding, and marries Constantius' sister, Helena. (She will die after five years of marriage-the fate of their issue, if any, is unknown.)

After his experience with Gallus, Constantius intends his representative to be more a figurehead than an active participant in events, so he at once packs Julian off to Gaul with a small retinue; Constantius' prefects in Gaul will keep him in check.

Julian, at first reluctant to trade his scholarly life for war and politics, will eventually take every opportunity to involve himself in the affairs of Gaul.