The 280's decade ran from January 1, 280, to December 31, 289.
- Roman usurper Proculus starts a rebellion at Lugdunum (Lyon, France), and proclaims himself emperor.
- Emperor Probus drives the Alans off to Asia Minor and suppresses the revolt in Gaul; Proculus is executed.
- The Germans destroy the Roman fleet on the Rhine; Bonosus is proclaimed emperor at Colonia Agrippina (Cologne).
- Probus defeats the army under Bonosus. Bonosus sees no way out and hangs himself. His family is treated with honours.
- 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.
- Roman territory is under constant threat of raids from Franks. The cities in Gaul are reinforced with defensive walls.
- 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.
- Emperor Probus returns to Rome, where he celebrates his triumph over the Vandals and the usurpers (Bonosus, Julius Saturninus and Proculus).
- Emperor Probus travels towards Sirmium (Serbia). He tries to employ his troops in peaceful projects, such as draining the swamps in Pannonia.
- Probus is murdered by his discontented troops. Marcus Aurelius Carus, an Illyrian and praetorian prefect, is proclaimed new emperor.
- Carus defeats the Quadi and Sarmatians on the Danube; for his victories he is given the title Germanicus Maximus.
- Carus appoints his oldest son, Marcus Aurelius Carinus, Caesar and co-emperor of the western Roman Empire.
- A new city is constructed in Fuzhou, slightly south of the original city Ye (the main street of the city has remained unchanged since that time).
- The Patriarch Theonas of Alexandria becomes one of the first bishops to use the title Pope.
- Emperor Carus travels through Thrace and Asia Minor; he invades the Persian Empire. After a long march he conquers Ctesiphon, the capital of the Persian kingdom, and presses on with the Roman army beyond the Tigris.
- Carus receives, for his victories in Persia, the title of Persicus Maximus.
- Carus dies in mysterious circumstances during the war against the Sassanids; during a violent dust storm he is killed by a stroke of lightning.
- Marcus Aurelius Carinus succeeds his father Carus.
- December – Numerian is proclaimed Emperor by his soldiers.
- November 20 – 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 – Diocletian, age 39, is proclaimed new emperor. He establishes himself at Nicomedia (modern İzmit, Turkey) and accepts the purple imperial vestments, claiming that the praetorian prefect (and rival for the throne) Arrius Aper murdered Numerian, killing him on the spot for the alleged deed. Diocletian carries out reforms of the Roman army, increasing conscription, and admitting large numbers of barbarian volunteers. In the winter he advances with his army across the Balkans.
- Sabinus Julianus, Roman usurper against Emperor Carinus, revolts in the Roman province of Pannonia on the edge of the Balkans. He invades northern Italy and declares himself emperor.
- The Bagaudae, a group of peasant insurgents, begin a revolt in Gaul against the Roman Empire.
- Diocletian declares the Dardani, a region located in Illyria, as a Roman province separate from Moesia.
- Early – Emperor Carinus marches from Britain to northern Italy, and defeats the army of the usurper Sabinus Julianus at Verona
- Summer – Battle of the Margus: Emperor Diocletian defeats the forces of Carinus in the valley of the Margus (Serbia)
- July 21 or July 25 – Diocletian appoints his fellow-officer Maximian to the office of caesar, or junior co-emperor
- Late summer – Diocletian defends the Danube against Sarmatian raids. He transfers his capital to Nicomedia (modern-day İzmit in Turkey).
- Carausius, naval commander at Bononia (modern-day Boulogne), is given the task of clearing the English Channel of Frankish and Saxon pirates
- Maximian is sent to pacify Gaul, where the Bagaudae, a band of peasants, are revolting against the Roman Empire
- April 1 – Emperor Diocletian elevates his friend Maximian to co-emperor, giving him the title Augustus. The Bagaudae are crushed, after their revolt in Gaul.
- Carausius, commander of the Classis Britannica, is accused of piracy and 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 barbarian mercenaries.
- Diocletian divides the empire in two, after economic and military problems. He gives Maximian control over the Western Roman Empire and appoints himself ruler of the Eastern Roman Empire (later known as the Byzantine Empire).
- Emperors Diocletian and Maximian become Roman Consuls.
- Diocletian signs a peace treaty with King Bahram II of Persia, and installs Tiridates III as king of Armenia.
- Diocletian re-organizes the Mesopotamian frontier, and fortifies the city of Circesium (modern Busayrah) on the Euphrates.
- September – The first Indiction begins.
- Emperor Diocletian conducts a military campaign in Raetia (Switzerland).
- Maximian builds, in Gaul, a Roman fleet to fight Carausius, usurper of Britain.
- Emperor Diocletian gains several victories along the Danube against the Sarmatians. He is given the honorable title of Sarmaticus Maximus.
- Maximian attempts to reconquer Britain from the usurper Carausius, but fails due to bad weather. He loses his fleet and accepts a peace treaty.
- Constantius Chlorus divorces his wife (or concubine) Helena, mother of Constantine I, and marries Emperor Maximian's stepdaughter, Theodora.
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- Saint George, Roman soldier and Christian martyr (approximate date)
- Yao Yizhong, Chinese general and warlord (d. 352)
- Eusebius of Vercelli, bishop and saint (approximate date)
- Ge Hong, Chinese taoist and government official (d. 343)
- Bonosus, Roman general and usurper
- Cen Hun, Chinese official and politician
- Julius Saturninus, Roman usurper
- Kang Senghui, Chinese monk and translator
- Maharaja Sri-Gupta of the Gupta dynasty
- Proculus, Roman usurper
- Jia Chong, Chinese statesman of the Jin dynasty (b. 217)
- Marcus Aurelius Probus, Roman emperor (b. 232)
- December 7 – Pope Eutychian
- Marcus Aurelius Carus, Roman emperor (b. 224)
- Shan Tao, Chinese taoist (b. 205)
- Carinus, Roman emperor
- Du Yu, Chinese general of the Jin dynasty (b. 222)
- Sabinus Julianus, Roman usurper
- Tuoba Xilu, chieftain of the Tuoba tribe and a member of the Xianbei people (present-day Mongolia)
- Crispin and Crispinian, patron saints of cobblers, martyred
- January 20 – Saint Sebastian, martyred
- Saint Maurice, Christian soldier (executed)
- Saints Victoricus, Fuscian, and Gentian, martyred
- Maximilian of Lorch, Christian missionary in the Roman province of Noricum
- Saint Sebastian, early Christian saint, martyr
- "List of Rulers of Korea". www.metmuseum.org. Retrieved 21 April 2019.
- "List of Rulers of Korea". www.metmuseum.org. Retrieved 20 April 2019.
- "Diocletian | Roman emperor". Encyclopedia Britannica. Retrieved 21 August 2018.
- "Saints Crispin and Crispinian | Christian saint". Encyclopedia Britannica. Retrieved 21 March 2019.
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