Centres of governance in the Roman Empire

All administrative, legal, fiscal, and military power in the Roman Empire was held by the Roman emperor and the centre of governance was at his location. Throughout the history of the empire multiple cities were used by the emperors as their place of residence, for minting coinage, or where they issued major legislation.

Rome was the centre until the Crisis of the Third Century and Tetrarchy, but returned to importance in the 5th century. Antioch, Nicomedia, Thessalonica, Sirmium, Trier, and Mediolanum were used as residences by multiple emperors in the 3rd and 4th centuries. Constantinople was dedicated by Constantine the Great in 330 AD and became the permanent seat of the emperor in the east starting with Theodosius I. After 312 AD no other emperor in that century resided in Rome and Ravenna was used as a residence by Honorius and Valentinian III, but the western emperors used both cities before the disposition of Romulus Augustulus.