The castle of the Knights of the Order of Saint John is situated at the entrance of Kos harbour on what used to be an island in antiquity, communicating with the inland through a bridge that one can still see even today namely the bridge of “Phoinikon” (Palm Trees) Avenue.
The castle consists of two defensive precincts. The interior one has four circular towers in the corners; the south-eastern tower forms part of the exterior precinct, which is the larger one of the two, with massive bastions on the four corners, battlements and gun ports. The two precincts are separated by a large moat and communicate with a drawbridge. The castle was built of local stone as well as parts of ancient buildings (columns, architraves, bases etc.) from the ruins of the ancient city. On the upper part of its masonry, one can see many blazons.
Over the main gate’ s one sees an Hellenistic frieze with masks and garlands. On the gates ceiling (the central gate, known as the Carmadino gate) there are basalt columns placed obliquely, which come probably from the early Christian basilica of Limenos. From travellers’ descriptions, we know that the interior precinct was built a little before the end of the 14th century when the sultan Bayazit I ‘s attacks on the city were becoming more intense.
The oldest remaining part of the castle is the circular tower to the left of the draw bridge, through which the two precincKos Island – Castle Air Viewts communicate, and bears the blazons of two Grand Masters: De Lastic (1437 – 1454) and De Milly (1454 – 1461). The exterior precinct is behind the interior, its construction began in 1495 by the Grand Master D’ Aubusson, continued by D’ Amboise and completed by Del Carretto in 1514. On the northern side, between the two precincts, there used to be a warehouse constructed by the knights; it was restored during the Italian occupation and today is a museum, where one can see altars, sculptures and inscriptions.