Known as the Castle of Kos, Nerantzias Castle owes its name to the fact that the city of Kos planted sour orange (nerantzies) and lemon trees in the late 14th and early 15th century. Nerantzias Castle on the Kountouriotis Coast was erected in the late 14th century as part of the fortification built by the Knights Hospitallers. It consisted of two fortified precincts, was rectangular in shape and each of the four corners were flanked by a tall tower.
For its creation they used a substantial number of architectural pieces of the ancient city of Kos and Asklipieion, which is visible in several parts to this day.
During the 19th century it functioned as the residence of the Turkish commander of the Turkish barracks and guard, while in March 1816 a large part of it was destroyed after an explosion in one of the gun powder cellar. Its current image is the work of the Italian Archaeological Service.