The Tower of Agios Petros is in the plain of Gavrios, in the small homonym settlement. It is one of the best-saved towers of Hellenistic period in Cyclades islands. It is dated from the 4th-3rd century BC and it is made from the local schist. It has five floors. It is cylindrical and the diameter of its base is 0,90m. Impressive is the spiral staircase that led to the other floors.