Petraeus (gr. Petraios) a friend of Philip V., king of Macedonia, who was sent by that monarch to Sparta in 220 BC, to receive the submission of the Lacedaemonians, and confirm them in their allegiance to Macedonia. We subsequently find him commanding a military force in Thessaly, where he successfully opposed the invasion of that country by the Aetolian general Dorimachus, 218 BC. (Polyb. iv. 24, v. 17.)