|Centuries:||2nd century – 3rd century – 4th century|
|Decades:||250s 260s 270s – 280s – 290s 300s 310s|
|Years:||281 282 283 – 284 – 285 286 287|
|284 by topic|
|State leaders – Sovereign states|
|Birth and death categories|
|Births – Deaths|
|Establishment and disestablishment categories|
|Establishments – Disestablishments|
|Ab urbe condita||1037|
|Chinese calendar||癸卯年 (Water Rabbit)
2980 or 2920
— to —
甲辰年 (Wood Dragon)
2981 or 2921
|- Vikram Samvat||340–341|
|- Shaka Samvat||205–206|
|- Kali Yuga||3384–3385|
|Iranian calendar||338 BP – 337 BP|
|Islamic calendar||348 BH – 347 BH|
|Minguo calendar||1628 before ROC
|Seleucid era||595/596 AG|
|Thai solar calendar||826–827|
Year 284 (CCLXXXIV) was a leap year starting on Tuesday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Carinus and Numerianus (or, less frequently, year 1037 Ab urbe condita). The denomination 284 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
- 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.