The Megalopolis Plateau is the second largest in Arcadia and extends around the city that bears its name. According to recent archaeological and geological research, during the Paleolithic era the area was densely forested, while at its center lay a large, cold lake. Megalopolis was founded in 370 BC at the urging of Epaminondas, after the Battle of Leuctra, as a unifying center for the Arcadians. Its purpose was to counter Spartan influence by bringing together inhabitants from neighboring Arcadian villages as well as runaway helots from Sparta.
When the Principality of Achaea—into which the Peloponnese was organized—was established in the early 13th century (1205–1209), it was divided into twelve feudal baronies. Among them, the barony of Veligosti stood out due to its strategic location and commercial activity. During this period, the renowned Castle of Karytaina was built; it would later, during the Greek Revolution, be used as a major stronghold by Theodoros Kolokotronis, strengthening the defensive line of the Greek forces in Arcadia.
Megalopolis does not appear to have played a central role during the Second Venetian Occupation (1685–1715), as Venetian strategic and political activity focused mainly on the coastal areas, where fortified ports and major cities were located. During the Ottoman period, the region was settled by Ottoman inhabitants, and a new settlement gradually formed around the ruins of the “Great City,” under the name Sinano. The name “Megalopolis” was officially restored in 1836. The modern Municipality of Megalopolis was created through the unification of the former municipalities of Gortyna, Megalopoli, and Falaisia. During the Revolution of 1821, the areas that now form the Municipality of Megalopoli served as important bases of the War of Independence. Karytaina became a strategic fortress for Kolokotronis, while Leontari functioned as a refuge and a center for mobilizing fighters for the battles of the Peloponnese. The wider region was the birthplace and field of action for several prominent figures of the Revolution, including Theodoros Kolokotronis, Nikitas Stamatelopoulos (Nikitaras), Grigorios Dikaios (Papaflessas), Panagiotis Kefalas, Christos Papageorgiou (Anagnostaras), Georgios Georgantas (Captain‑Georgaros), and many more.