...also known as the Castle of Neratzia, was built by the Knights of the Order of Saint John, right in the center of Kos’ harbor, to protect the town from imminent Ottoman attacks.
The knights were occupying the island, together with the rest of the Dodecanese, since 1315, and it took them about 130 years to construct the castle, finally completing it in 1514. It was built with local stone and with various assorted of ancient ruins.
One can observe on the structure many blazons, columns, bases and architraves from the ruins of the old city as well as the Asclepeion.