It is also called the castle of the Chora of Kalymnos. It covers the wide summit of a steep and mountainous mound that is located at a short distance to the north-east of the settlement at an altitude of 255 m. The resistant castle walls enclose a surface of 30,500 sq. meters. It was the main residential centre of the island during the Middle Ages and, more specifically, during the period of the Knights. Its current form including high walls that embrace peripherally the summit of the rocky mound dated back to the end of the 15th century, after the reconstruction of the fortification by the Knights of Saint John, who occupied the Dodecanese from 1309 to 1522. The castle, though, already existed and it was possibly constructed during the middle Byzantine period (10th -11th century). After its expansion and rebuilding, it was organized and constituted the residential centre of Kalymnos.
It is estimated that in its interior the settlement could accommodate approximately 1,000 residents. The occupation of the castle continued until the beginning of the 18th century. It was then that because of the gradual increase of the population and the restriction of piracy, the castle-residence was gradually abandoned and its residents moved out to the current settlement of Chora of Kalymnos.