Built in the 6th century BC , partly dismantled in the 6th century AD to build a chapel, and of late reconstructed slowly, partly by dismantling the chapel. A mile from the village of Ano Sangri, out in the country.
The ruins of this Byzantine castle are southeast of Ano Sangri,, high on a bluff; its fall to Marco Sanudo after a two month siege led to 350 years of Venetian rule, with Naxos a Venetian duchy.
The 13th century summer home of the Venetian duke, Marco Sanudo (ruler of the Cyclades during the first part of the Venetian period), built on top of a peak near Geometric era and Mycenaean tombs, about an hour's walk from the village of Halki, and less from Potamia.. Though mostly crumbled, the views from up there are superb, especially in spring, when all is green.
Most of the Byzantine chapels/churches on Naxos date from the 9th to the 15th centuries. Restoration has often revealed several layers of frescoes, with more recent ones removed intact and then preserved, often in the Byzantine Museum in Athens. The 5th or 6th century Panayia Dhrossiani Located below the mountain village of Moni. (above Halki) has some of Naxos' best frescoes. Visitors ring the bell to get the caretaker's attention, as there are no regular hours. The 8th century church of Ayios Mamas sits in a low valley below the road that goes from Hora to Sangri, accessible by path from the village of Kato Potamia, which also has a fine church of its own, though mostly locked. This village, the lower of the three Potamia villages, features a rather fine large church of its own as well, though it is often locked. Ayios Mamas the patron saint of animals. One can walk right into the church, with its packed earth floor and high dome. Fine marble decorations are seen around the openings that appear to have been windows, with faint traces of frescoes discernible here and there in the walls. In spring, the field in front of it full of wildflower. On a hill just above it is an old Jesuit seminary, its yard now used to keep someone's chickens. The small Byzantine chapel of Ayios Ioannis Yiroulas, is located in Ano Sangri, built over an ancient temple of Dhimitra (Demeter). West of Sangri on the road to Halki is the Kaloritsa chapel ,accessible only on foot, with frescoes dating to the 10th century. The 11th century church of Panayia Pantanassa ,behind the waterfront in Hora, up some steps, was once part of a Byzantine monastery, and known for its early icon of the Virgin. In Halki are two very fine frescoed churches: the 12th century Panayia Protothronis and the 9th century Ayios Diasoritis (out in a field to which you can walk from Halki); another wonderful church is just off the road near the village of Kerami, in 'Metohi'. In Filoti are the churches of Koimisis tis Theotokou, with a carved marble iconostasis, and the Panayia Filotissa, with a marble steeple.