The castle of Kos, the most imposing monument in the city, stands at the entrance to the harbour. It was built by the Knights of the Order of St John of Jerusalem, who captured the island in 1314 and held it until 1522, when it fell to the Turks The castle occupied a strategic position in that, together with the castle of Halikarnassos on the coast of Asia Minor opposite, it gave them control of the sea lanes.