Independent castle, used as a surveillance post, built on rising ground 4 km NW of Pothia harbour. It is also known as Pera Kastro. It is roughly diamond-shaped in plan, facing south, with the other sides mostly secured by the steepness of the rocky ground. The main gate was on the N side, but access was also possible through the south wall. Another gate on the east side of the south wall was later in date. On the masonry of the semicircular tower of the south side are the arms of Fantino Querini, Hospitaller governor of Cos, and of grand master Jean de Lastic (1437-1454). On the south wall may be seen the arms of the Order of St. John and of Knight Fra Juan Geltru, governor of Cos after 1466. According to G. Gerola (1913), there were also to be seen the arms of Adhemar Dupuy (1464-1466), J. Geltru, of Antoni Fluvian or J. de Lastic and of Querini. The castle, with the windmills, was the personal property of the castellan, who lived there. It is believed that it was constructed by Querini (1436-1453), who incorporated it into the island's defences. Records of a court case brought by the locals against Querini, who was forcing them to provide labour for the construction of probably this castle in 1445, still survive; the case was won by Querini.