In Roman mythology, Pan's counterpart Faunus was one of the oldest Roman deities, the di indigetes, who was a good spirit of the forest, plains, and fields; when he made cattle fertile he was called Inuus. He was consulted as a god of prophecy, under the name of Fatuus, with oracles in the sacred groves of Tibur, around the well Albunea, and on the Aventine Hill in ancient Rome itself (Peck 1898). The responses were said to have been given in Saturnian verse (Varro, L. L. vii. 36). Faunus revealed the future in dreams and voices that were communicated to those who came to sleep in his precincts on the fleeces of sacrificed lambs.

A goddess of like attributes, called Fauna and Fatua, was associated in his worship. She was regarded sometimes as his wife, sometimes as his sister. As Pan was accompanied by the Paniskoi, or little Pans, so the existence of many Fauni was assumed besides the chief Faunus (Peck 1898). In fable Faunus appears as an old king of Latium, son of Picus, and grandson of Saturnus, father of Latinus by the nymph Marica. After his death he is raised to the position of a tutelary deity of the land, for his many services to agriculture and cattle-breeding.

Faunus was known as the father or husband or brother of Bona Dea (Fauna, his feminine side) and Latinus by the nymph Marica (who was also sometimes Faunus' mother). Fauns are place-spirits (genii) of untamed woodland. Educated Romans connected their fauns with the Greek satyrs, who were wild and orgiastic drunken followers of Dionysus, with a distinct origin.

The Christian writer Justin Martyr identified him as Lupercus ("he who wards off the wolf"), the protector of cattle, following Livy, who named his aspect of Inuus as the god who was originally worshiped at the Lupercalia, celebrated on the anniversary of the founding of his temple, February 15, when his priests (Luperci) wore goat-skins and hit onlookers with goat-skin belts. The Faunalia was another festival in Faunus' honor; it took place on December 5. Two festivals, called Faunalia, were celebrated in his honour--one on the 13th of February, in the temple of Faunus. on the island in the Tiber, the other on the 5th of December, when the peasants brought him rustic offerings and amused themselves with dancing (Peck 1898).

A euhemeristic account made of Faunus a Latin king, son of Picus and Canens. He was then revered as the god Fatuus after his death, worshipped in a sacred forest outside what is now Tivoli, but had been known since Etruscan times as Tibur, the seat of the Tiburtine Sibyl. He was associated with wolf skins, wreaths and goblets.

In Dionysiaca by Nonnos, Faunus/Phaunos accompanied Dionysos when the latter campaigned against the Indians.