But Valentine's Day most likely had its origins in the annual Lupercali festival of the Romans, which was celebrated on February 15th. On this day, hunters would ritualistically slay both a female goat and a dog with a knife. The bloody knife was then drawn across the foreheads of two noble-born children. The children were then to laugh, indicating they had received magic protection against wolves and wolfmen. The god Lupercus would then inspire the men to behave like wolves, and they would go through the city snaring women with whips.

Happy Valentine's Day!

-Wikipedia.org: St. Valentine's Day
-Fate Magazine: From Werewolves with Love: The History of Valentine's Day