The pileus (Ancient Greek: πῖλος, pîlos; also pilleus or pilleum in Latin) was a brimless felt cap worn in Ancient Greece, Etruria, Illyria (especially Pannonia), later also introduced in Ancient Rome. The pileus also appears on Apulian red-figure pottery.
The pilos together with the petasos were the most common types of hats in Archaic and Classical era (8th–4th century BC) Greece. In the 5th century BC, a bronze version began to appear in Ancient Greece and it became a popular infantry helmet. It occasionally had a horsehair crest. The Greek pilos resembled the Roman and Etruscan pileus, which were typically made of felt. The Greek πιλίδιον (pilidion) and Latin pilleolus were smaller versions, similar to a skullcap.