Megalopolis, a city of ancient Greece, ori-ginally capital of the Arcadian confederation, on the river Helisson. It was founded at the suggestion of Epaminondas, after the battle of Leuctra (371 B. C), and was designed by him as a check to Sparta. Forty townships furnished inhabitants for the new city, which was 6 m in circumference, and had a larger domain allotted to it than that possessed by any Arcadian State. But it never attained the importance anticipate. for it, and was too large for its population, that of its entire territory being but 65,000. Apprehension of Sparta afterward drove the Megalopolitans into alliance with the Macedonians, and held them aloof from the coalition formed in Greece on the death of Alexander for the recovery of independence. They at length fell under the dominion of tyrants, the last of whom, Lydiades, resigned in 234, and united Megalopolis to the Achaean league. In 222 Cleomenes III., king of Sparta, captured it by surprise, and destroyed the greater part of it; but after his defeat at the battle of Sellasia (221) the Megalopolitans who had fled returned under the conduct of Philopoemen, and rebuilt the city on the original scale; but it never regained its former prosperity, and rapidly sank into insignificance.
It contained no acropolis, owing to its flat situation, but a magnificent agora, colossal statues, and famous temples. Little remains of this great city, which used to be called the great desert, owing to its magnificent distances, excepting the well preserved ruins of the theatre, which Pausanias regarded as the largest in Greece; and they are still visible amid the thickets and corn fields which cover the site of the city near the village of Sinano.