From the middle of the second century CE, The Roman Empire faced increasing Germanic tribe infiltration along the Danubian and Rhine borders, and internal political chaos. Without efficient imperial succession, Romans in from the third century set up generals as emperors, who were quickly deposed by rival claimants. Facilitating further territorial losses to Barbarian tribes, this continued until Diocletian (r. 284-305). He and Constantine (324-337) administratively reorganized the empire, engineering an absolute monarchy. Cultivating a secluded imperial tenor, Constantine the Great patronized Christianity, particularly in his new city Constantinople, founded on the ancient site of Byzantium. Christianization, in the Hellenized and Mediterranean cities and among certain Barbarian newcomers, proceeded with imperial support, and became the state religion under Theodosius (r. 379-95). Germanic tribal invasions also proceeded, as did battles with the Sassanids in the East. From 375 Gothic invasions, spurred by Hunnic marauding, began en masse, particularly in Danubian, Balkan areas. Entanglement with imperial armies resulted in Roman defeats, and increased migration into Roman heartlands as far as Iberia. The Empire, as military and bureaucracy, underwent a certain Germanization. From the death of Theodosius, the Eastern Empire followed its own course, evolving into the Hellenized Byzantine state by the seventh century, as repeated sackings of Latin Rome (410, 455), contraction of food supplies to the West, and deposition of the last Western Emperor (Romulus Augustulus) by the Ostrogoth Odovacar (476), ended any hope of recovering Pax-Romana in the Mediterranean basin. Gaul was controlled by a shifting patchwork of tribes.
But though the Empire itself no longer existed, through the Christian Church, through the always idealized vision of glorious Rome, and through the political structures that evolved out of Rome's carcass, vestiges of the Empire played vital and identifiable roles in the formation of the early Medieval European world.