 Constantine received a formal education at Diocletian 's court , where he learned Latin literature , Greek , and philosophy . The cultural environment in Nicomedia was open , fluid and socially mobile , and Constantine could mix with intellectuals both pagan and Christian . He may have attended the lectures of Lactantius , a Christian scholar of Latin in the city . Because Diocletian did not completely trust Constantius — none of the Tetrarchs fully trusted their colleagues — Constantine was held as something of a hostage , a tool to ensure Constantius 's best behavior . Constantine was nonetheless a prominent member of the court : he fought for Diocletian and Galerius in Asia , and served in a variety of <unk> ; he campaigned against barbarians on the Danube in 296 AD , and fought the Persians under Diocletian in Syria ( 297 AD ) and under Galerius in Mesopotamia ( 298 – 299 AD ) . By late 305 AD , he had become a tribune of the first order , a <unk> <unk> primi . 
