The castle of Rio was built in 1499 by Sultan Vajazet II on the ruins of the ancient temple of Poseidon. It was used as a fortress, alongside Antirrio, for the war operations against the Venetians.
In 1532, Admiral Adria Doria was captured and destroyed by the Genoese, but the Ottomans recaptured and rebuilt it in the same year. In 1687 Francis Morozini besieged the castle of Rio and occupied it, but was forced to reconstruct it after the siege caused great damage to the walls.
Then new towers were added and the castle took the form it has today. The castle was re-occupied by the Ottomans in 1715, when it was also used as a prison. In 1828 he was surrendered to the French under General Meazon, and from 1831 until 1912 he was converted into a military and political prison.
