The Castle of Koskinas (or Castle of Nikaria or Castle of Mesaria), is located in the village of Kossoikia, at the centre of the island. It was built by the Byzantines in the 10th c. AD on the top of a conical hill and was the strongest defence work of the byzantine city Doliche (ancient Oinoe). The small area it occupies attests its use by a small military force, commissioned to control the surroundings and the sea routes from this privileged position. The fortification wall that encircles the summit of the hill is only partially preserved. The main entrance is located at the north side of the wall. The Post-Byzantine church of Agios Georgios (Saint George) "Dorganas" in the interior of the fort, is a single-nave, barrel-vaulted basilica. At the north-west slope, beneath the castle, traces of a settlement are preserved. The castle was reinforced when Icaria came under the rule of the Genoese (1362-1481), but was later abandoned when they left for Chios, under the threat of the Ottoman advance. Subsequently, the Hospitaller Knights of Rhodes ruled Icaria until the mid-16th c., when the Ottomans expanded to the Aegean. The history of the castle has been preserved until today through local legends and medieval folk poems, such as the "Riva tou Kastrou tis Nikarias" (Rhyme of the Castle of Nikaria), which describes the capture of the island?s castles by the Genoese.