After Antigonus had taken Tegea by siege, and had surprised Orchomenus and Mantineia, Cleomenes, now reduced to the narrow confines of Laconia, set free those of the Helots who could pay down five Attic minas (thereby raising a sum of five hundred talents), armed two thousand of them in Macedonian fashion as an offset to the White Shields of Antigonus, and planned an undertaking which was great and entirely unexpected.
Megalopolis was at that time of itself fully as large and strong as Sparta, and could have assistance from the Achaeans and from Antigonus; for Antigonus was encamped near by, and it was thought that the Megalopolitans were chiefly responsible for his being called in by the Achaeans.
This city Cleomenes planned to snatch away (for nothing else could better describe the speed and unexpectedness of his famous achievement), and ordering his men to take five days' rations, he led them forth to Sellasia, as though he would ravage the territory of Argos. But from there he descended into the territory of Megalopolis, and after giving his men their supper at the Rhoeteium, he marched at once by way of Helicus against the city itself.
When he was not far away he dispatched Panteus with two divisions of Lacedaemonians, ordering him to seize a portion of the wall between two towers which he had learned was the most unprotected part of the walls of Megalopolis, while he himself with the rest of his army followed slowly after. Panteus found not only that particular spot, but also a great part of the wall, undefended, and at once tore down some portions of it, undermining others, and slaying all the defenders whom he encountered. Cleomenes promptly joined him, and before the Megalopolitans were aware of it, he was inside the city with his army.