Gardiki Castle is a 13th-century Byzantine castle on the southwestern coast of Corfu and the only surviving medieval fortress on the southern part of the island. It was built by a ruler of the Despotate of Epirus, and was one of three castles which defended the island before the Venetian era (1401–1797). The three castles formed a defensive triangle, with Gardiki guarding the island's south, Kassiopi Castle the northeast and Angelokastro the northwest
The castle is located on a low hill near the village of Agios Matthaios which is situated at a higher elevation. The ruler responsible for the construction of the castle is not known, but it is assumed that it was built either by Michael I Komnenos or his son Michael II Komnenos, rulers of the Despotate of Epirus. Immediately to the south of the castle lies Korissia Lake which is separated from the sea by a narrow strip of land.
Remains from the upper Paleolithic era, dating from 20,000 BC., when Corfu was still united to the mainland region of Epirus, were found on the site of the castle at the rock shelter of Grava Gardikiou, including hunter-gatherer stone tools and animal bones, which have since been removed and are exhibited at the Archaeological Museum of Corfu.
The walls of Gardiki Castle form an octagon and the structure features eight strong towers decorated by rows of tiles. There are elements from an ancient structure which have been incorporated into the construction of the castle. The ancient structure was probably a fountain-house.
The eight towers are square in shape and the outline of the octagonal structure is almost elliptical. At the top of the southern tower there are traces of a chapel with remnants of religious frescoes of portraits of saints. Although in a state of disrepair, the towers still retain their full height. The castle entrance is preserved but the interior is in a state of ruin.
References:Bomarsund fortress and garrison was built in 1832-1854 by Russian Empire to defence Ă…land Islands against enemies. British and French fleet attacked against it during the Crimean War in 1854. After a week of fighting the British stormed the remaining fort. Anglo-French forces destroyed it totally after battle. In the Treaty of Paris 1856, the entire Ă…land Islands were demilitarized, which is a status that has been preserved until this day.
Nowadays there are some ruins left and fortress area is open for visitors.