all dates are BCE unless otherwise noted
Megalopolis was the last major Greek city to be established before the decline of ancient Greece, and was born out of the ashes of war at the wrong time in history. The name Megalopolis itself is indicative of the grandiose symbolism created by a once great but waning culture, and surely enough its glory would be short lived.
It was founded in 371, out of a consortium of smaller villages in Arcadia. Sparta and Thebes had for generations been engaged in a tug of war for influence in the region, with Sparta holding the upper hand until the Battle of Leuktra, in 370. There, forces led by the Theban general Epaminondas defeated the Spartans, and the commander moved quickly to consolidate power in a central location. He chose the valley of Arcadia, in a low-lying spot with some irregular hills, straddling the north and south banks of the Helisson River. With promises of protection, settlers were cajoled into making their homes there. Megalopolis was named the capitol of the Arcadian Confederation (comprising the villages in the valley and surrounding mountains) in 368, but this distinction was nominal at best. While it occupied key strategic territory, none of its residents actually had roots there, and many simply wanted to go back to their own towns.
The city walls were built using the surrounding hills as an outline. Within them, according to the 2nd century (CE) Greek historian Pausanias, were individual residences, a council house where the city's democratic business was conducted (featuring an image of Ammon), a race track, a theatre, an agora, and sanctuaries in honor of Aphrodite, Ares, Dionysus, Artemis, Asclepius, Heracles and Hermes, and Apollo, Hermes and the Muses. All built thanks to the generosity of the big-hearted Thebans who came all the way down from the northeast over rough terrain to lend a hand.
Arcadians' loyalty to Thebes was fickle, however, and Thebes was only slightly less brutal than Sparta. In 362, half of the Arcadian alliance headed by Megalopolis fought against Thebes, to secure the right of Megalopolis residents to return to their original homes. But the Spartan threat was ever-present. Arcadia knew it needed a protector, so it never bit too hard at whatever hand served that role. Thebes helped turn back a Spartan attack again in 353, but when the next one came, in 331, it was no longer the dominant northern power, having been eclipsed by Macedonia during the time of Philip and Alexander. Megalopolis, it seems, wasn't too picky in its alliances, and with the help of the new outsiders managed to repel siege after siege, dispersing to traditional homelands in times of peace and returning to the fortified city when the Spartans came a-knocking. This kept up until 223, when the Spartan king Cleomenes III dealt the Arcadians a decisive blow, utterly wrecking the city walls. By 175, again according to Pausanias, unspecified outsiders were again offering to help rebuild Megalopolis, but we don't know if that offer was ever taken up. We can only presume that, with Rome already ascendant, it wouldn't have been the same.