: 4th century BC
- 3rd century BC
- 2nd century BC
Decades: 330s BC 320s BC 310s BC 300s BC 290s BC - 280s BC - 270s BC 260s BC 250s BC 240s BC 230s BC
285 BC 284 BC 283 BC 282 BC 281 BC 280 BC 279 BC 278 BC 277 BC 276 BC 275 BC
- Battle of Heraclea: The Greeks, led by Pyrrhus of Epirus, defeat with severe casualties a Roman army the first time these cultures meet in battle.
- Aristarchus uses the size of the Earth's shadow on the Moon to estimate that the Moon's radius is one-third that of the Earth.
- Achaean League refounded.