In Greek mythology, Priapus was a minor rustic fertility god, protector of livestock, fruit plants, gardens and male genitalia. Priapus is marked by his oversized, permanent erection, which gave rise to the medical term priapism.

He became a popular figure in Roman erotic art and Latin literature, and is the subject of the often humorously obscene collection of verse called the Priapeia.

In this fresco the 'Priapus with Caduceus' or 'Priapus-Mercury' is a male figure with the beard and giant erect phallus of Priapus walking away with the caduceus and winged sandals of Mercury (apparently the humour was to see Priapus thieving from the god of thieves, but both are gods of fertility and abundance). Museo Archeologico Nazionale, Naples, Italia.