The Monastery of Zygos (Frankish castle) is located just outside of Holy Mount Athos. It is a Byzantine monastery belonged to Mt Athos and was established in the middle of the tenth century, while it was destroyed just before 1198. All of its fortified courtyard survives, reinforced with ten towers, which surrounds an area of 5.5 stremma. The Catholicon, a building dating back to the first quarter of the 11th century, survives up to a height of 4 meters. It is a church in the cross-in-square style with two burial chapels and evident are four building phases. The 10th Ephorate of Byzantine Antiquities performs a systematic excavation aimed to bring to light and study the building history of the middle-Byzantine monastery of Zygos, as mentions Archaeologist Ioakeim Ath. Papaggelos.