The most impressive ancient monument is the White Tower (Άσπρος Πύργος), a Hellenistic marble watchtower (ca. 300 BC) with walls preserved to 2 m. and an interior staircase, standing on a hilltop just east of the road from Chora to Mega Livadi, near Mega Chorio. Work began in 2011 to study the fallen blocks for an eventual reconstruction.
At least four other ancient towers have been located, including the megalithic Psaros Pyrgos (Ψαρός Πύργος) or "Couch of the Cyclops" in the SW corner of the island. The so-called "Castle of the Old Lady" (Κάστρο της Γριάς) above Ganema and Koutalas preserves scant remains of a collapsed dry-stone construction in a notch below the twin rocky summits. Rough fragments of white marble and roof tile, and archaic fine-ware potsherds on the SE terraces of the hillside, suggest the existence of an ancient sanctuary.
The Monastery of Taxiarchs
The fortified Monastery of the Taxiarchs, dedicated to the Archangels Michael and Gabriel, was built in 1572 just E of the village of Galani. The sole monk is Archimandrite Makarios, who entered the monastery as a youth in 1958 and continues to maintain it with admirable devotion.