The hill of the medieval Castle is the cell of the city from the period of the first habitation (fourth millennium B.C.) until today. The Castle was built by the Venetian duke of Naxos Sanoudos (13th century) with architectural parts of ancient temples. The archaeologists have discovered that in the Castle there are walled up the parts of three archaic temples and two of the classical period of the ancient city. From those it is saved only a small part of the archaic temple of Athena (6th century B.C.) on the top of the hill. Next to the foundations of the temple a part of the early Cycladic village was revealed. During our walk in the castle we will meet small churches, many of them embodied in the walls, like the Panagia of the Cross (1514), Saint Anna, Saint Marcos, Saint Stylianos and the astonishing from an architectural view temple of Saint Constantine with a roofed courtyard and splendid view towards the sea, one of the most remarkable in the Aegean Sea.