Castle overlooking the settlement of Mandraki in the NE part of the island, on the coast. It was the strongest medieval castle of Nissyros, and is also known as Panayia Spiliani from the venerable monastery inside it. It was built in two stages, one Hellenistic, the other Hospitaller. On the SW side there are remnants of Hellenistic structures and a rectangular tower. The oldest part of the Hospitaller defences begins at the entrance with the arms of grand master J. de Milly (1454-61). The walls were strengthened by grand master G. B. degli Orsini (1467-1476); a flanking tower was added to the east wall. A number of coats of arms may be seen on the fortifications, including those of Milly, Orsini, Aubusson and members of the Calvi and da Corogna families, at different times feudal lords of the island. In 1471, under threat by the Ottoman fleet, the castle was evacuated and the inhabitants of the settlement were taken to Rhodes. An unsuccessful Turkish attack is recorded in 1504 and in 1522 the island passed into the hands of the Turks.