Valentine's Day derives from a Christianized version of a pagan holiday. Lupercalia was an ancient, I think it was even pre-Roman, festival, observed on February 13 through 15, to avert evil spirits and purify the city, releasing health and fertility.

In Roman mythology, Lupercus is a god sometimes identified with the Roman god Faunus, who is the Roman equivalent of the Greek god Pan.

Lupercus is the god of shepherds. His festival, celebrated on the anniversary of the founding of his temple on February 15, was called the Lupercalia.