The end of the Tetrarchy
According to the rules of the Tetrarchy, the Augusti Diocletianus and Maximianus retired in 305 AD. The Caesares, Galerius and Constantius Chlorus (or Constantius I), became the new Emperors, while Flavius Valerius Severus and Galerius Maximinus (better known as Maximinus Daia) became the new Caesars. Soon however the tetrarchic system started to collapse, with various competitors and usurpers striving for the titles of Caesar and Augustus. In 306 AD Constantius Chlorus died in York and was succeeded by Severus as Augustus. The son of Constantius Chlorus, Flavius Valerius Constantinus (the future sole Emperor Constantine), became Caesar. He resided in Britain and Gaul.
Still in 306 AD Marcus Aurelius Valerius Maxentius (the son of Maximianus and son-in-law of Galerius) also made a bid for power. He resided in Rome and gained control of Italy, Sardinia and Corsica, Sicily and North Africa. In 308 AD he was confronted with a short-lived revolt in North Africa led by Domitius Alexander, causing an interruption of the grain supply of Rome and food riots. There were violent conflicts between the rulers, and Maxentius strengthened the wall of Aurelianus around Rome. Maximianus appeared on the scene again, Licinius was a new competitor.
Some stability was achieved in 312 and 313 AD. In 312 Constantine defeated Maxentius in the Battle at the Pons Milvius (Milvian Bridge) in Rome. In 313 Licinius defeated Maximinus Daia in a battle on the Black Sea. From now on Constantine ruled in the western half of the Empire, Licinius in the eastern half, both as sole rulers. A few years later there was already a first military conflict between the two. Licinius was defeated decisively in 324 AD. Constantine was now the sole Augustus, with his son Constantius (the Second) as sole Caesar. Constantine's reign would last until 337 AD.
The Milvian Bridge in the north of Rome. Photo: Wikimedia, Daniela Marina Tagliafico.The Battle at the Milvian Bridge is famous because of a preceding vision and dream of Constantine, instructing him to fight with the support of a Christian symbol.[1] In 313 AD, with the so-called Great Persecution by Diocletian fresh in the memory, Constantine and Licinius issued the Edict of Milan, a proclamation of religious tolerance. It granted freedom to all religions, but focused on Christianity. It assured Christians of legal rights, including the right to organize churches, and ordered the return to Christians of confiscated property. It was an extension of an edict issued two years earlier by Galerius, the Edict of Serdica. Lactantius in De mortibus persecutorum ("On the Deaths of the Persecutors") transmitted the text of the Edict of Serdica and of the Edict of Milan.
Constantine's vision and the Battle at the Milvian Bridge depicted in a 9th-century manuscript. Photo: Bibliothèque nationale de France.In Ostia clear traces are documented of both the struggle between Maxentius and Constantine, and of Constantine's attitude towards Christians.
(1) For the "In hoc signo vinces" vision and dream see: Richard Flower, "Visions of Constantine", The Journal of Roman Studies 102 (2012), 287-305.
