A well-known castle city, located in the southwestern end of Peloponnese. It begun its development in the 7th century AD, and the castle itself was built by the Venetians, at the end of the 13th century. It is an excellent example of Venetian fortress building.

The caste is square shaped, with two lines of walls. On the tallest point, in the western side of the castle, sits the acropolis, and the southern side ends at the sea, defended by rock formations. The main entrance that used to lead in the town inside the castle is a large square gate, on the northern side, and on the northeastern side is a large wall, pieces of which are still preserved. In the place of the first Byzantine castle now is a nunnery.

In 1209, the Venetians took control of Koroni and built a second outer courtyard that had four times the size of the other. They fortified it with towers and battlements, and reinforced the other fortifications of the castle. Inside it, there were houses and shops that were later destroyed.

In the eastern side of the castle, there was a second line of defence, destroyed later during the siege laid by Morosini. In the western side of the castle, there is a fortress built by the Venetians in 1463 that was destroyed and rebuilt in 1685. Today, in that spot remains an octagonal tower of Turkish build.

Inside the castle there is the Byzantine church of Saint Sophia, built in the 12th century.

In 1500, the Turks took control of Koroni. Later, in 1532, the knights of the Order of Malta along with the navy of emperor Charles II conquered it, but it was taken back by the Turks in 1534. At that time, around 2000 residents migrated to lower Italy.

In 1685, the Venetians took the castle back, but the Turks retook it in 1715. In 1770, during the Orlov Revolt, it was almost completely destroyed by bombardments. Finally, in 1828, Marshal Nicolas Joseph Maison, commander of the French expeditionary corps in the Morea, conquered the castle and later gave it to the Greeks.

Today, two families live in the castle, and more houses still remain around, along with a nunnery, olive trees and vineyards.

Entrance is free, but not all parts of the castle are accessible.