Lupercalia

The general Festival of Juno Februa, meaning "Juno the purifier "or "the chaste Juno", was celebrated on February 13–14. While Lupercalia was a festival local to the city of Rome observed February 13–15.

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Many think this festival is what sprang into Valentine's Day. Due to the rise of Christianity in Europe many so called pagan festivals was often renamed for and dedicated to the early Christian saints. The Catholic Church was thought to even keep so of the same traditions in Saint Valentines day.

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Eve of Lupercalia 

February 14th used to be a Roman custom, the Eve of Lupercalia, and was primarily a festival of fertility. The tradition in Rome was to hold what was effectively a lottery, where boys and girls were paired off with each other at random.The young women would then gather in the city and their names were put in boxes. These "love notes" were called "billets." The men of Rome would draw a billet, and the woman whose name was on it became his sexual lust partner with whom he would fornicate until the next Lupercalia or February 14th. Thus, February 14th became a day of unbridled sexual lust. Many of these pairings evolved into firm friendships and even marriages. Throughout the following days of the feast other traditions including ritual sacrifices, bathing in blood, and whipping in the streets was practiced.

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Lupercalia Day 

Lupercalia was a Roman festival dedicated to Lupercus who was the god of the shepherds, the hunter of wolves. It was observed on February 15 to avert evil spirits and purify the city, releasing health and fertility.

The religious ceremonies were directed by the Luperci, the "brothers of the wolf (lupus)", a corporation of priests of Faunus, dressed only in a goatskin, imitating the god, Lupercus or Pan.

The festival began with the sacrifice by the Luperci (or the flamen dialis) of two male goats and a dog. Next, two young patrician Luperci were led to the altar, to be anointed on their foreheads with the sacrificial blood, which was wiped off the bloody knife with wool soaked in milk. The two Luperci would run around Palatine Hill while holding  a goatskin thong called a "februa." Women would sit all around the hill, as the blood covered priests would strike them with the februa to make them fertile.

"Lupercalia, of which many write that it was anciently celebrated by shepherds, and has also some connection with the Arcadian Lycaea. At this time many of the noble youths and of the magistrates run up and down through the city naked, for sport and laughter striking those they meet with shaggy thongs. And many women of rank also purposely get in their way, and like children at school present their hands to be struck, believing that the pregnant will thus be helped in delivery, and the barren to pregnancy." - Plutarch • Life of Caesar