How a decisive mountain clash ended Spartan dominance and forced a king into exile
In 222 BC, the Battle of Sellasia pitted the Macedonian-led Achaean League against the forces of King Cleomenes III. By fortifying the rugged terrain of Laconia, the Spartans hoped to hold their ground, but superior numbers and a daring cavalry charge ultimately shattered their defense, forever altering the Peloponnesian power structure.
By 229 BC, Cleomenes III had transformed Sparta into the preeminent power of the Peloponnese, successfully challenging the Achaean League. As the conflict escalated, the Achaean leader Aratus of Sicyon sought military intervention from Antigonus III Doson of Macedon. The price of this alliance was steep: the Achaeans were forced to surrender the strategic fortress of Acrocorinth to the Macedonians. This shift in regional dynamics was further complicated when Ptolemy III of Egypt withdrew his financial support from Sparta, leaving Cleomenes struggling to pay his mercenary forces.
The climax occurred in the summer of 222 BC at Sellasia. Cleomenes occupied the heights of Mount Olympus and Mount Evas, creating a formidable defensive position. Antigonus arrived with a massive coalition force of 29,200 men, including phalangists, peltasts, and various allied contingents. The battle remained deadlocked until the Arcadian cavalryman Philopoemen executed an unauthorized charge that relieved the pressure on the allied infantry. This maneuver allowed the Macedonians to overwhelm the Spartan positions on the hills.
The defeat was catastrophic for the Spartan military. Of the 6,000 Spartiates engaged, only 200 survived, as many chose death over surrender. Cleomenes fled to Alexandria, where he remained in exile until his death three years later. Following the victory, Antigonus entered Sparta, marking the first time a general from outside the city had successfully occupied it. The battle effectively ended the Spartan resurgence and cemented Macedonian influence over the region.
Source: Battle of Sellasia
