The castle was the acropolis of the unwalled settlement of Chorio, on the NE part of the island at a height of 154 metres, on the site of an ancient acropolis. There are three distinct building phases: Hellenistic, Byzantine and Hospitaller. The castle covers an area of 1,250 square metres with a perimeter of 140 metres. Of this perimeter today survive the south and east walls, part of the Hellenistic defences and Byzantine walls with Hospitaller additions. To the NE stands a round tower, while a plain semicircular bastion is the only feature which may be securely assigned to the Hospitaller period. It preserves the arms of grand master Emery d?Amboise (1503-1512) and the order of the Hospital with the date 1507. The main gate is located in the middle of the east walls. IThere are three churches within the defences: the church of Our Lady (Panayia Kyra) with its cistern, of St. Michael Tharrinos and of the Great Virgin. The arms of master Philibert de Naillac are mounted on the castle gate. The arms of grand masters Jacques de Milly (1454-1461) and Pere Ramon Zacosta (1461-1467) also survive, as do those of Fra Antoine Virieu (1456). Symi was one of the first islands to fall into the hands of the knights of St. John after the conquest of Rhodes (1306-1309). In 1407 grand master Philibert de Naillac carried out repairs on the castle. Florentine traveller Cristoforo Buondelmonti mentions the castle in 1420. Some repairs on the castle are dated to the years 1454 -1461; while in 1457 an Ottoman attack on Symi is mentioned. In 1460 the castle was plundered by ta force of 7,000 Turks. In 1485 and 1504 came two further Ottoman raids and in 1522 the island with its castle surrendered to the Turks.