It was built in the early 1220s by the Crusader rulers of the Principality of Achaea as their main stronghold, and is perhaps the finest fortification of the early period of Frankish rule in Greece preserved in the country today. The castle is located on a small plateau above sea level, and comprises a central hexagonal keep, built around an inner courtyard and containing two-storeyed halls along its entire length, and complemented by an outer wall enclosing an outer yard on its western side. The castle is largely preserved in its original 13th-century state, with only minor later modifications for the installation of artillery.