Which 222 BCE battle ended Cleomenes III’s reign in Sparta?

The Battle of Sellasia in 222 BCE ended Cleomenes III’s reign in Sparta. The Macedonian king Antigonus III Doson defeated Cleomenes and his Spartan allies near the northern approaches to Laconia.

Cleomenes had carried out major political and social reforms in Sparta, including redistributing land, cancelling debts, and attempting to restore a larger citizen body. His expansion brought Sparta into conflict with the Achaean League and Macedonia. Antigonus assembled a coalition and invaded the Peloponnese.

After the defeat at Sellasia, Cleomenes fled to Egypt, where he later died. Antigonus occupied Sparta but did not simply erase its institutions. The battle marked a decisive decline in Sparta’s independent power during the Hellenistic period, long after the city’s classical military dominance had ended.