Chronology of the emperors of the late Roman Empire ((284–325) Tetrarchy and start of Constantinian dynasty) by Meyer Ed.

Diocletian 20 November 284 – July 285 (in competition with Carinus) July 285 – 1 April 286 (alone) 1 April 286 – 1 May 305 (as Augustus of the east, with Maximian as Augustus of the west)

285

After the deaths of Carus and his son Numerian on campaign in Persia, Diocletian was proclaimed emperor. The title was also claimed by Carus' other surviving son, Carinus, but Diocletian defeated him in the Battle of the Margus. Diocletian's reign stabilized the empire and marks the end of the Crisis of the Third Century. He appointed fellow officer Maximian as Augustus, co-emperor, in 286.

Maximian (April 1, 286 AD – May 1, 305)

286

He shared the latter title with his co-emperor and superior, Diocletian, whose political brain complemented Maximian's military brawn. In late 285, he suppressed rebels in Gaul known as the Bagaudae. From 285 to 288, he fought against Germanic tribes along the Rhine frontier. Together with Diocletian, he launched a scorched earth campaign deep into Alamannic territory in 288, temporarily relieving the Rhine provinces from the threat of Germanic invasion.

Constantius I 293–305 (as Caesar with Maximian); 305–306 (as Augustus in the west, with Galerius as Augustus in the east)

293

As Caesar, he defeated the usurper Allectus in Britain and campaigned extensively along the Rhine frontier, defeating the Alamanni and Franks. Upon becoming Augustus in 305, Constantius launched a successful punitive campaign against the Picts beyond the Antonine Wall. However, Constantius died suddenly in Eboracum (York) the following year. His death sparked the collapse of the tetrarchic system of government inaugurated by the Emperor Diocletian.

'Tetrarchy', or "rule of four"

Period: 293 to 325

Diocletian delegated further on 1 March 293, appointing Galerius and Constantius as Caesars, junior co-emperors. Under this 'tetrarchy', or "rule of four", each emperor would rule over a quarter-division of the empire. Diocletian secured the empire's borders and purged it of all threats to his power.

Galerius (305 - 311)

305

During his reign he campaigned, aided by Diocletian, against the Sassanid Empire, sacking their capital Ctesiphon in 299. He also campaigned across the Danube against the Carpi, defeating them in 297 and 300. Although he was a staunch opponent of Christianity, Galerius ended the Diocletianic Persecution when he issued an edict of toleration in 311.

Severus II(Summer 306 – March/ April 3)

306

Adopted as junior co-emperor ('Caesar') and heir by Constantius I Chlorus in 305 AD; succeeded as Augustus in 306; opposed by Maxentius and Constantine I

Constantine (July 25, 306 – May 22, 337 )

306

Son of Constantius I Chlorus, proclaimed emperor by his father's troops; accepted as Caesar (west) by Galerius in 306 AD; promoted to Augustus (west) in 307 AD by Maximian after death of Severus II; refused relegation to Caesar in 309 AD

Maxentius (October 28, 306 – October 28, 312)

306

Son of Maximian, seized power in 306 after death of Constantius I Chlorus, in opposition to Severus and Constantine I; made Caesar (west) by Maximian in 307 AD after the death of Severus

Licinius I (November 11, 308 – September 18, 324)

308

For most of his reign he was the colleague and rival of Constantine I, with whom he co-authored the Edict of Milan that granted official toleration to Christians in the Roman Empire. He was finally defeated at the Battle of Chrysopolis, and was later executed on the orders of Constantine I.

War of Constantine and Maxentius

Period: 310 to 313

Maximinus II(May 1, 311 – July/August 313)

311

Nephew of Galerius, adopted as Caesar and his heir in 305 AD; succeeded as Augustus (shared with Licinius I) in 311 AD

War of Licinius and Maximinus Daia

Period: 311 to 313

Meanwhile, to the east, on Galerius’ death in 311 the eastern provinces were divided between Maximinus Daia and Licinius. Daia was unhappy that Licinius had been made senior emperor by Galerius, and took the first available opportunity to declare himself as emperor. Licinius held the eastern European provinces, while Daia took possession of the Asiatic provinces.

Battle of the Milvian Bridge October 28, 312

Period: 312 to 312

The Battle between the Roman Emperors Constantine I and Maxentius on October 28, 312. It takes its name from the Milvian Bridge, an important route over the Tiber. Constantine won the battle and started on the path that led him to end the Tetrarchy and become the sole ruler of the Roman Empire. Maxentius drowned in the Tiber during the battle; his body was later taken from the river and decapitated, and his head was paraded through the streets of Rome on the day following the battle.

Edict of Milan in 313

Period: 313 to 313

Constantine was the first Roman emperor to convert to Christianity,and he played an influential role in the proclamation of the Edict of Milan in 313, which declared religious tolerance for Christianity in the Roman empire.

Wars of Constantine and Licinius

Period: 320 to 325

First Council of Nicaea (Sunday 20 May to Saturday 19 June, AD 325)

Period: 325 to 325

Constantine I organized the Council along the lines of the Roman Senate and presided over it, but did not cast any official vote. This ecumenical council was the first effort to attain consensus in the Church through an assembly representing all of Christendom. Hosius of Corduba, who was probably one of the Papal legates, may have presided over its deliberations.