Fresco of Priapus, House of the Vettii, Pompeii

In Greek mythology, Priapus (Πρίαπος) was a minor rustic fertility god of purely phallic character, protector of livestock, fruit plants, gardens and male genitalia. (Roman equivalent: Mutinus Mutunus.) He was a son of Aphrodite, with Dionysos, or with Adonis (according to a scholiast on Lycophron, noted by Kerenyi 1951). At Helicon in Boeotia, the travel-writer Pausanias pointed out a statue of Priapus that was "worth seeing":

"This god is worshipped where goats and sheep pasture or there are swarms of bees; but by the people of Lampsacus he is more revered than any other god, being called by them a son of Dionysus and Aphrodite." (Description of Greece IX.312)

Sculptures of Priapus with large, ithyphallic genitalia were placed in gardens and fields to guarantee an abundant crop. For the Romans, his statue was used as a scarecrow and his erect penis was thought to frighten thieves. Epigrams collected in Priapeia show Priapus using sodomy as a threat toward transgressors of the boundaries he protected like a herm:

"I warn you, my lad, you will be sodomised; you, my girl, I shall futter; for the thief who is bearded, a third punishment remains."

"... If I do seize you . . . you shall be so stretched that you will think your anus never had any wrinkles."

The sacrifices in honor of Priapus, Jacopo de' Barbari

The sacrifices in honor of Priapus, Jacopo de' Barbari

The Latin collection of Priapeia shows how poets invented comic and obscene situations for him, giving him more literary prominence than he enjoyed in rites or cult, though masked phallic figures were prominent on many festive occasions, both in Greece and in the wider Roman world. In Ovid's Fasti (6.319ff), the nymph Lotis fell into a drunk slumber at a feast, and Priapus seized this opportunity to advance upon her. With stealth he approached, and just before he could embrace her, Silenus's donkey alerted the party with "raucous braying." Lotis awoke and pushed Priapus away, but her only true escape was to be transformed into the lotus flower. To repay the donkey for spoiling his opportunity, Priapus slaughtered him. In later versions of the story, Lotis is replaced with the virginal goddess Hestia. Ovid's anecdote served to explain why, in the city of Lampsacus on the Hellespont, where Priapus was worshipped among the offspring of Hermes (Hyginus, Fabulae, 160), donkeys were sacrificed.

Lucian (De saltatione) tells that in Bithynia Priapus was accounted a warlike god, a rustic tutor to the infant Ares.

One of the most famous images of Priapus is that from the House of the Vettii in Pompeii; it is a wall fresco in which Priapus is weighing his phallus against a bag full of money and it appears that his phallus is heavier.

The medical condition priapism gets its name from Priapus.

Priapus is also recognized as a saint in Ecclesia Gnostica Catholica.

Reference

Gods of the Greeks, Carl Kerenyi

Priapeia, sive diversorum poetarum in Priapum lusus or Sportive Epigrams on Priapus, translation by Leonard C. Smithers and Sir Richard Burton