Citadel of St Andrew: In the hill of St Andrew in the northeast part of the island there are some ruins of a fortified settlement of Early Cycladic period (3rd Millenium BC). The settlement flourished during the Mycenaean period and continued to be inhabited during Geometrical and Archaic times. The structuring of the citadel took place in the 12th century BC when it was fortified by a double Cyclopean wall. In that wall additions had been made in the following years and it is visible until today.
Ancient towers: Relics of 57 ancient towers of Classical and Hellenistic times have been found. The external diameter of the towers was 8 meters and they were used as observatories and as storage spaces. They are found in the tops of the hills and on hillsides.
Settlement of Kastro: This settlement is continuously inhabited since Middle Cycladic period. There are some relics of the Venetian fort (14 century AD). There are also some remains of the medieval residencies built in the outer part in order to form part of the fortification. The houses are built one next to each other leaving a few spaces for common use. They are two stories or three stories whilst there are some bigger houses towards the center of the settlement.