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The Roman Empire at the end of the Third Century was a turbulent place in which to live with dangerous enemies both to the North and to the East. In addition, there were internal rebellions and troubles to deal with and Diocletian began to realise that changes would have to be made if the empire was to survive. In the late Third Century, a revolt broke out in Gaul and the current emperor Diocletian sent Maximianus, a tough army general, to put down the rebellion.
The first change that Diocletian made was to appoint another emperor to help him to manage the empire and his choice was Maximianus. So, Diocletian then ruled the Eastern empire whilst Maximianus took control of the West.
Diocletian also wanted to improve the way that power was transferred on the death of the incumbent emperor. This period had always been accompanied by power struggles and unrest, so the plan was that each Emperor (or Augustus) would appoint a Caesar (emperor-to-be) so that the Caesars could acquaint themselves with government and eventually smooth the takeover of power. The idea was that Diocletian and Maximianus would rule for twenty years and then abdicate allowing the Caesars to take over the running of the Empire. Diocletian chose Galerius as Caesar and Maximianus chose Constantius Chlorus. These four rulers therefore made up what was known as the Tetrarchy. Diocletian was based at Nicomedia in Asia Minor whilst Maximianus governed from Milan. Galerius chose Thessalonika and Constantius Chlorus set up court in Trier.
305 AD was the time for Diocletian to abdicate and in due course the two new Augusti each chose a new Caesar. Constantius chose Severus II whilst Galerius selected Maximinus, but problems lay ahead. Diocletian had made the Tetrarchy work successfully through strong leadership but in 306 AD, Constantius Chlorus died and the British Legions elevated his son, Constantine I, to the throne. To avoid civil war, Galerius, the remaining Augustus agreed to name Constantine as Caesar and Severus II was made up to the new Augustus.
The Tetrarchy; A.= Augustus; C. = Caesar. Emperor West Reign Emperor East Reign Maximianus C. 285-286, A. 286-305, 307-310 Diocletian A. 284-305 Constantius Chlorus C. 293-305, A. 305-306 Galerius C. 293-305, A. 305-311 Constantine I C. 306-308, A. 308-337 Maximin C. 305-308, A. 308-313 Severus II A. 306-307 Maxentius A. 307-312 Licinius A. 308-324
At this point, Galerius, despite being ruler in the east, attempted to extend his provincial taxation policy to Rome itself. Roman citizens had been exempt from paying tax since the days of the Republic and the result was rebellion. As a result, the Senate and Praetorians duly elected Maxentius, the son of Maximianus and son-in-law of Galerius, as Caesar. Maxentius invited his father to help him rule and in 306/307 AD he defeated the army of Severus II at Ravenna, so the Roman Empire was now being ruled by four Augusti and a Caesar. Civil war looked inevitable but in 308 AD, Diocletian came out of retirement and arranged a peace conference at Carnuntum on the Danube frontier. The outcome of this was that Maximianus again abdicated, Constantine was demoted to Caesar, Licinius was made Augustus in the west and Maxentius was declared an enemy of the state.
Maxentius managed to hold onto power for a further four years, by which time Galerius had died and Constantine had formed an alliance with Licinius. Constantine made plans to invade Italy and met Maxentius at the Battle of the Milvian Bridge on October 28th, AD 312. The army of Maxentius was routed and Maxentius was thrown from the Milvian Bridge into the Tiber, drowning as a result of the weight of his armour.
At the places mentioned so far, the Romans minted coins at Nicomedia and Thessalonika (from 249 AD until its closure by Leo I) and Trier (from c. 291 - 430 AD). Maxentius opened the mint at Ostia in 308/309 AD where it operated until May 313 AD. These facts are known from mint marks which began to appear on coins from the middle of the 3rd Century. Maxentius, Maximianus, Galerius, Maximinus II, Licinius I and Constantine I all appear on Ostian mint-marked coins together with Romulus about whom little is known. He was the son of Maxentius, acted as Consul in 308 and 309 AD, dying in 309 AD. He appears on a number of coins minted at Ostia which have on their reverse face a domed temple surmounted by an eagle.
( In "Roman Ostia", Meiggs makes reference to an early Republican mint at Ostia in the 3rd Century BC. Mattingley bases his evidence for the existence of this mint on a very large hoard of early asses found 'near Ostia'. He describes the mint as having closed at the beginning of the 2nd Punic War, and that coins from this mint circulated mainly in Etruria and Cisalpine Gaul.)