The Battle of Sellasia took place in 222 BC during the Cleomenic War between the forces of the Spartan king Cleomenes III and the Achaean League, led by Antigonus III Doson of the Macedonian Kingdom. The battle occurred near the town of Sellasia in the Peloponnese, Greece, and was a significant conflict in the struggle for control over the region. In this battle, Antigonus's forces decisively defeated Cleomenes, leading to the decline of Spartan power. The victory allowed the Achaean League to strengthen its influence in the Peloponnese, marking a pivotal moment in the history of ancient Greek city-states.