Fortress of the 4th c. B.C. that controls the highland pass between Attica and Boeotia. It is situated about 1 km SW of the ancient demos of Phyle. It has an irregular elliptical plan measuring 95x30 m. Its wall, which reaches up to sixteen courses in height, is constructed in the isodomic system and runs round part of the hill, at the north , east and south sides, as the precipitous west and southwest sides were left unwalled. The main gate, which has collapsed, is located on the eastern side, while still stand the smaller southern gate with its lintel. The fortress is defended by means of four impressive towers all extending beyond the outer perimeter of the wall, three of which are rectangular and one circular. The circular one is the most imposing of all, with a diameter of 6 m, and protected the most vulnerable northern side. The ruins of a few buildings, probably intended to house the garrison, can be discerned inside the fortress.