Winter: Emperor Galerius wins his third and final victory over the Sarmatians.
April: In Rome, Emperor Maximian attempts to depose his son Maxentius, but the soldiers in Rome side with Maxentius and force Maximian to flee to the court of Constantine I.[1]
Constantine raids the territory of the Bructeri and builds a bridge across the Rhine at Cologne.
November 11 – The Conference of Carnuntum: Attempting to keep peace within the Roman Empire, Galerius recalls Diocletian briefly from retirement, and they convene with Maximian. Diocletian persuades Maximian to return to retirement, and he and Galerius declare Maxentius a public enemy. Licinius is proclaimed Augustus of the west, while rival contender Constantine I is again declared Caesar.
Bereft of his father's support, Maxentius increasingly presents himself as the Conservator Urbis Suae (Preserver of His Own City). Construction of the Basilica of Maxentius (or Basilica Nova), the largest building in the Roman Forum, is begun.
Maxentius institutes toleration of the Christians in his territories.