66 BCCenturies: 2nd century BC - 1st century BC - 1st century
- Catiline accused of conspiring against the Roman Republic with Autronius and the younger Sulla.
- The alliance between Mithridates VI of Pontus and Tigranes I of Armenia is broken.
- Battle of the Lycus - Pompey the Great decisively defeats Mithridates VI, effectively ending the Third Mithridatic War.
- Comet Halley passed earth.