Megalopolis is on the great western plain of Arcadia, which is aobut 30km (18.6miles) long from north to south and about 16km (9.92miles) wide, and an average altitude of 427meters (1400feet), with a more temperate climate than that of the plain of Tripoli. It is also wooded and watered by the Alpheios river, and encircled by mountains.
The modern town, which is situated on either side of a tributary of the Alpheios-the Hellison-- is quite small, with a population of around 6,000 inhabitants. It is the chief town in its district and also the capital of the federated states of Arcadia. The appearance of the town is marred seriously by two large power stations (with pollution from the hydroelectric plant killing the oak trees), and like Tripoli, there is also a strong military presence. There is a second river to the north of the modern city, called by three names: the Elissonas, Barboutsiana, and Daria River. The city is singularly lacking in amenities for travellers, such as hotels or food, unless some of these have materialized very recently.
The ancient city, to the north 1km (.62 miles) is one of the most extensive and least touristic sites in the Peloponnese. It was built at the junction of the two rivers, and was an important administrative and military center during a period of general decline in Greece, during the early 4th century BC. Its name means 'Great City'.
The site is open Tues-Sun, 8:30am-3pm and is free. The construction of the city, from 371-368BC, was overseen by the Theban leader Epaminondas, and was one of the most ambitious of such projects during the Classical age. Intended to be the strongest link in a chain of Arcadian settlement, a strategic barrier designed to hold back the Spartans, it failed in this purpose, despite its nine km of walls. Its citizens, who had been imported from forty local villages, ended up returning home, the Spartans attacked it sporadically. In 362BC, after the breakup of the Arcadian confederation, half of the Arcadians allied themselves with the Spartans against Thebes. Sacked in 223BC by Kleomenes III, two thirds of the population escaped to Messenia. Within two centuries, it was ruined and abandoned. It finally disappeared after a Slav invasion.