337 CE - The Roman Empire at the death of Constantine the Great

Constantine continued many reforms begun by Diocletian and further split serval provinces into smaller units.
306 CE - Constantine is hailed emperor at Eburacum (York), controls Spain, Gaul, Germany and Britain
312 CE - Constantine defeats Maxentius at the Milvian Bridge, gains control of Italy, Raetia and North Africa
316-317 CE - Constantine conquers the dioceses Pannoniae and Moesia from Licinius
324 CE - Constantine defeats Licinius and gains entire empire for himself