Megalopoli (Greek: Μεγαλόπολη) is a town in the southwestern part of the regional unit of Arcadia, southern Greece. It is located in the same site as ancient Megalopolis (Μεγαλόπολις). When it was founded in 371 BC, it was the first large urbanization in rustic Arcadia. Its theater had a capacity of 20,000 visitors, making it one of the largest ancient Greek theaters. Megalopoli has several schools, shops, churches, hotels and other services.
Megalopoli is situated in a wide valley, surrounded by mountains: the Taygetus to the south, the Mainalo to the north, the Tsemperou to the southeast and the Lykaion to the west. Its elevation is 430 m above sea level. The river Alfeios flows through this valley, coming from the east and flowing to the north, passing south and west of the town. Its tributary Elissonas passes north of the town. The large lignite deposits around Megalopoli are being exploited by open-pit mining. The Megalopoli Power Plant, 3 km northwest of the town centre, has produced electricity from this lignite since 1969.