225 BCCenturies: 4th century BC - 3rd century BC - 2nd century BC
- Seleucus III Ceraunus succeeds his father Seleucus II Callinicus as king of the Seleucid dynasty.
- Battle of Faesulae, Romans are defeated by the Gauls of Northern Italy.
- Erastothenes of Cyrene calculates the circumference of the Earth.
- Apollonius of Perga writes On Conic Sections and names the ellipse, parabola, and hyperbola.
- State of Qin conquered the state of Wei in China.