22 Tetrarchy

The Tetrarchy is the term adopted to describe the system of government of the ancient Roman Empire instituted by Roman Emperor Diocletian in 293, marking the end of the Crisis of the Third Century and the recovery of the Roman Empire. The government of the empire was divided between the two senior emperors, the augusti, and their juniors and designated successors, the caesares.

Allectus was a Roman-Britannic usurper-emperor in Britain and northern Gaul from 293 to 296.

Marcus Aurelius Mausaeus Carausius was a military commander of the Roman Empire in the 3rd century. He was a Menapian from Belgic Gaul, who usurped power in 286, during the Carausian Revolt, declaring himself emperor in Britain and northern Gaul. He did this only 13 years after the Gallic Empire of the Batavian Postumus was ended in 273. He held power for seven years, fashioning the name "Emperor of the North" for himself, before being assassinated by his finance minister Allectus.

Constantine I, also known as Constantine the Great, was a Roman emperor from 306 to 337. Born in Naissus, Dacia Mediterranea, he was the son of Flavius Constantius, an Illyrian army officer who became one of the four emperors of the Tetrarchy. His mother, Helena, was Greek and of low birth. Constantine served with distinction under emperors Diocletian and Galerius campaigning in the eastern provinces against barbarians and the Persians, before being recalled west in 305 to fight under his father in Britain. After his father's death in 306, Constantine was acclaimed as emperor by the army at Eboracum (York). He emerged victorious in the civil wars against emperors Maxentius and Licinius to become sole ruler of the Roman Empire by 324.

Constantine II was Roman emperor from 337 to 340. Son of Constantine the Great and co-emperor alongside his brothers, his attempt to exert his perceived rights of primogeniture led to his death in a failed invasion of Italy in 340.

Constantius I was a Roman emperor. He ruled as Caesar from 293 to 305 and as Augustus from 305 to 306. He was the junior colleague of the Augustus Maximian under the Tetrarchy and succeeded him as senior co-emperor of the western part of the empire. Constantius ruled the West while Galerius was Augustus in the East. He was the father of Constantine the Great and founder of the Constantinian dynasty. After his death he became known as Chlorus, but the nickname does not appear in records before the sixth century.

Flavius Julius Crispus was the eldest son of the Roman emperor Constantine the Great and his junior emperor (caesar) from March 317 until his execution by his father in 326. The grandson of the augustus Constantius I, Crispus was the elder half-brother of the future augustus Constantine II and became co-caesar with him and with his cousin Licinius II at Serdica, part of the settlement ending the Cibalensean War between Constantine and his father's rival Licinius I. Crispus ruled from Augusta Treverorum (Trier) in Roman Gaul between 318 and 323 and defeated the navy of Licinius I at the Battle of the Hellespont in 324, which with the land Battle of Chrysopolis won by Constantine forced the resignation of Licinius and his son, leaving Constantine the sole augustus and the Constantinian dynasty in control of the entire empire. It is unclear what was legal status of the relationship Crispus's mother Minervina had with Constantine; Crispus may have been an illegitimate son.

Diocletian was a Roman emperor from 284 to 305. Born to a family of low status in Dalmatia, Diocletian rose through the ranks of the military to become a cavalry commander of the Emperor Carus's army. After the deaths of Carus and his son Numerian on campaign in Persia, Diocletian was proclaimed emperor. The title was also claimed by Carus's surviving son, Carinus, but Diocletian defeated him in the Battle of the Margus.

Lucius Domitius Domitianus was a Roman usurper against Diocletian, who seized power for a short time in Aegyptus.

Lucius Domitius Alexander, probably born in Phrygia, was vicarius of Africa when Emperor Maxentius ordered him to send his son as hostage to Rome. Alexander refused and proclaimed himself emperor in 308.

Galerius was Roman emperor from 305 to 311. 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 Serdica in 311.

Marcus Aurelius Sabinus Julianus was a Roman usurper against Emperor Carinus or Maximian. It is possible that up to four usurpers with a similar name rebelled in a timeframe of a decade, but at least one of them is known by numismatic evidence.

Valerius Licinianus Licinius was Roman emperor from 308 to 324. For most of his reign he was the colleague and rival of Constantine I, with whom he co-authored the Edict of Milan, AD 313, 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.

Licinius II, also called Licinius Junior and Licinius Caesar, was the son of the Roman emperor Licinius I. He held the imperial rank of caesar between March 317 and September 324, while his father was augustus, and he was twice Roman consul. After losing a civil war, his father lost power and both he and Licinius the Younger were eventually put to death.

Martinian, who died in 325, was Roman Emperor from July to September 18, 324. He had been appointed co-emperor by Licinius.

Maxentius was Roman emperor from 306 to 312. He was the son of former Emperor Maximian and the son-in-law of Emperor Galerius. The latter part of his reign was preoccupied with civil war, allying with Maximinus II against Licinius and Constantine. The latter defeated him at the Battle of the Milvian Bridge in 312, where Maxentius, with his army in flight, purportedly perished by drowning in the Tiber river.

Maximian, nicknamed Herculius, was Roman emperor from 286 to 305. He was Caesar from 285 to 286, then Augustus from 286 to 305. He shared the latter title with his co-emperor and superior, Diocletian, whose political brain complemented Maximian's military brawn. Maximian established his residence at Trier but spent most of his time on campaign. 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.

Galerius Valerius Maximinus Daza was Roman emperor from 310 to 313. He became embroiled in the Civil wars of the Tetrarchy between rival claimants for control of the empire, in which he was defeated by Licinius. A committed pagan, he engaged in one of the last persecutions of Christians.

Various lists regarding the political institutions of ancient Rome are presented. Each entry in a list is a link to a separate article. Categories included are: constitutions (5), laws (5), and legislatures (7); state offices (28) and office holders ; political factions and social ranks (8). A political glossary (35) of similar construction follows.

The Portrait of the Four Tetrarchs is a porphyry sculpture group of four Roman emperors dating from around 300 AD. The sculptural group has been fixed to a corner of the façade of St Mark's Basilica in Venice, Italy since the Middle Ages. It probably formed part of the decorations of the Philadelphion in Constantinople, and was removed to Venice in 1204 or soon after.

Flavius Valerius Severus, also Severus II, was a Roman emperor from 306 to 307. After failing to besiege Rome, he fled to Ravenna. It is thought that he was killed there or executed near Rome.

Aurelius Valerius Valens was Roman Emperor from late 316 to March 1, 317. Valens had previously been dux limitis in Dacia.