The tower at Aghios Petros on Andros dates from the Hellenistic period (4th-3rd centuries B.C.) and is one of the best preserved towers in the Cyclades. It is cylindrical, made of local schist, with a diameter of 9.40 m. at the base and a height of almost 20 m. A winding staircase leading to five, at least, storeys, is preserved inside the building.

The tower is located at a commanding position over the plain of Gavrion and has a wonderful view to the sea. Around the monument are preserved installations for the extraction of metals (copper) used as late as the beginning of our century. There is evidence, though, of similar activity in antiquity. The tower was evidently used for the control of the surrounding land and the sea.