A Culture Ministry statement says the stone torso of a man in armor and the head of a bearded man were found during an underwater survey in September at Mandraki, on western Kythnos.
The statement said Thursday it was unclear whether the head matched the torso, which stands some 4.5 feet (1.4 meters) high. They date from the era of Rome's control of Greece, between 146 B.C. and A.D. 330.
Both pieces were found 8 feet (2.5 meters) deep, and had been reused during ancient times as building material for a wall protecting the harbor. Previous surveys at Mandraki have located submerged piers and building material.
Kythnos lies about 60 miles (100 kilometers) southeast of Athens.