From Barbara Walker’s The Woman’s Encyclopedia of Myths and Secrets
The original Valentine’s Day on the Ides of February was Rome’s Lupercalia, a festival of sexual license. Young men chose partners for erotic games by drawing “billets” — small papers — with women’s names on them. Christians denounced these prototypical valentines as “heathens’ lewd customs.” Churchmen tried to substitute saints’ names and short sermons on the billets, but people soon reverted to the old love-notes. February was sacred to Juno Februata, Goddess of the “fever” (febris) of love. The church replaced her with a mythhical Saint Valentine, who was endowed with several contradictory biographies. One of them made him a handsome Roman youth, executed at the very moment his sweetheart received his billet of love.
St Valentine became a patron of lovers perforce, because the festival remained dedicated to lovers despite all official efforts to change it. Even in its Christianized for, the Valentinian festival involved sex worship, called “a rite of spiritual marriage with angel in the nuptial chamber.” Ordinary human beings engaged before witnesses in an act of sexual intercourse described as the marriage of Sophia and the Redeemer. A spoken formula said, in part, “Let the seed of light descend into thy bridal chamber, recei the bridegroom … open thine arms to embrace him. Behold, grace has descended upon thee.”
During the Middle Ages, St. Valentine was much invoked in love charms and potions, since he was a sketchily Christianized version of such love-gods as Eros, Cupid, Kama, Priapus, and Pan.