Ovrios is a rather unknown uninhabited island in the Saronic Gulf, near the Isthmus of Corinth.
The isle has traces of habitation since prehistoric times. Various points of the island were used during the Mycenaean era, the early Byzantine period, as well as during the Venetian period and the Ottoman domination.
The fortification, which is distinct from a distance, for the most part is a construction of the 17th-18th century and probably Venetian, a remnant of the 2nd Venetian domination. There are also parts of the fortification that belong to the Early Byzantine period.