Probus defeats the army under Bonosus. Bonosus sees no way out and hangs himself. His family is treated with honours.[2]
Julius Saturninus, governor of Syria, is in Alexandria, charged with the defense of the East. He is declared emperor and withdraws to Apamea. Probus besieges the city and puts him to death.[3]
Roman territory is under constant threat of raids from Franks. The cities in Gaul are reinforced with defensive walls.[4]
Emperor Wu of the Jin dynasty completes the unification of China, which was previously divided between three contending powers during the Three Kingdoms period. The Jin dynasty's capital of Luoyang becomes a thriving centre of commerce as foreign diplomats and traders travel there.[5]
The praetorian prefect Marcus Aurelius Carus usurps power in Raetia. Probus attempts to organise a campaign against Carus but is murdered by his discontented troops in Sirmium.
Carus defeats the Quadi and Sarmatians on the Danube; for his victories he is given the title Germanicus Maximus.
Exploiting the Persian civil war, Carus leaves Carinus in charge of much of the Roman Empire and, accompanied by his younger son Numerian, invades the Sassanid Empire. They sack Seleucia and Ctesiphon, the capital of the Persian kingdom, and they press on beyond the Tigris. For his victories, Carus receives the title of Persicus Maximus.[citation needed]
The officer Diocles, the future Emperor Diocletian, distinguishes himself in the war against the Persians.[citation needed]
Carinus campaigns with success in Britain and on the Rhine frontier.[citation needed]
Summer: Carus dies in mysterious circumstances during the war against the Persians. Various sources claim he died of illness, was struck by lightning or was killed in combat.[citation needed]
Carinus and Numerian succeed their father Carus. Numerian, who had accompanied his father into the Persian Empire, leads the army back to Roman territory.[citation needed]
Emperor Numerian travels through Bithynia (Asia Minor) on his way home to Rome. Suffering from an inflammation of the eyes, he travels in a closed litter in which soldiers find his decaying corpse.
November 20 – The commander of Numerian's domestici (household troops), Diocles, is chosen to be the new emperor. In a military assembly outside Nicomedia (modern İzmit, Turkey), Diocles claims that the praetorian prefect (and rival for the throne) Arrius Aper murdered Numerian, and he personally stabs and kills the prefect on the spot. The new emperor changes his name to the Latinised 'Diocletian'. Building on existing trends, Diocletian presents his rule as that of a god-like dominus or autocrat.
Sabinus Julianus, the praetorian prefect of Emperor Carinus, exploits the instability and usurps the throne in northern Italy.
King of Kings Bahram II installs Mirian III, of the House of Mihran, on the throne of the Kingdom of Iberia. Mirian would rule the kingdom until his death in c. 361.
Summer – Battle of the Margus: Emperor Diocletian defeats the forces of Carinus in the valley of the Margus (Serbia). Numerous soldiers desert Carinus during the battle. Carinus then flees to the Pannonian fort of Cornacum, but he is soon slain by his officers.
July 21 or July 25 – Diocletian appoints his fellow-officer Maximian to the office of caesar, or junior co-emperor.
Winter/Spring: The CaesarMaximian defeats the Bagaudae rebellion in Gaul. He then defeats a Germanic invasion into Gaul, defeating an army of Burgundians and Alemanni and another army of Chaibones and Heruli.
Emperor Diocletian campaigns successfully against Sarmatian raids. The future emperor Constantius defeats the 'Bosporian Sarmatians'.
April 1 – Diocletian rewards Maximian by elevating him to co-emperor, giving him the title Augustus.
Summer: Carausius, commander of the Classis Britannica, is accused of piracy by Maximian and is sentenced to death. He responds by declaring himself emperor of Britain and Northwestern Gaul. His forces consist of the newly built Roman fleet and three legions in Britain. The Carausian Revolt is supported by Gaulish merchant ships and Frankish mercenaries.
On the same day that he is made consul, Maximian launches a campaign against an invasion of Gaul by the Alemanni. After defeating this invasion, he then invades Alemannia itself, entering across the Upper Rhine and returning to Roman territory via the Upper Danube.
Around this time, the future emperor Constantius defeats and captures a Germanic king, the latter having prepared an ambush against the Romans.
Diocletian signs a peace treaty with King Bahram II of Persia, and installs the pro-Roman Arsacid Tiridates III as king over the western portion of Armenia.
Diocletian re-organizes the Mesopotamian frontier, and fortifies various locations including the city of Circesium (modern Busayrah) on the Euphrates. Around this time, he begins the construction of the Strata Diocletiana. Throughout his reign, similar fortification efforts are conducted on the other frontiers as well, with fortifications constructed or restored behind, on and beyond the borders. Conscription and the number of legions increase, although the legions themselves are reformed into smaller and more flexible units. At some point in time, Diocletian may have also established the late Roman military system of Comitatenses (field army units) and Limitanei (border units), but some scholars date this development to the reign of Constantine I (r. 306–337).
Around this time, an army loyal to Maximian, probably led by the future emperor Constantius, defeats the usurper Carausius or his Frankish allies in northern Gaul. In this or the following year, Carausius withdraws his military forces and administrative presence from Gaul, confining himself to Roman Britain.
Maximian makes an alliance with the Frankish king Gennobaudes.
Far from Carausius' fleet, in the rivers of Gaul, Maximian builds a fleet to contest control of the North Sea and re-take Britain.
Around this time, Constantius marries Maximian's stepdaughter, Theodora, and it may also be around this time that the general Galerius marries Diocletian's daughter Galeria Valeria.
In this or the following year, Emperor Diocletian campaigns with success against the Sarmatians. The future emperor Galerius may have distinguished himself during this campaign. [14]
In this or the following year, Maximian attempts to reconquer Britain from the usurper Carausius but is defeated at sea. [15]
^Hornblower, Simon (9 November 2023). "Ancient Rome". Britannica. Retrieved 11 November 2023.
^Lotha, Gloria (9 August 2020). "Wudi". Britannica. Retrieved 11 November 2023.
^Jones, A.H.M; Martindale, J.R.; Morris, J. (March 2, 1971). The Prosopography of the Later Roman Empire: Volume 1, AD 260-395. Cambridge, England: Cambridge University Press. p. 977.
^Yarshater, Ehsan; Fisher, William Bayne, eds. (1968). "Iran under the Sasanians". The Cambridge History of Iran. Vol. 3. Cambridge: Cambridge University Press. p. 128. ISBN978-0-52106-935-9.
^Thomas, P. C. (1992), A Compact History of the Popes, Mumbai: Bombay Society of St Paul, p. 19, ISBN978-8-17109-142-3
^Cousin, Jean. "Diocletian". Encyclopædia Britannica. Retrieved February 23, 2024.