Valentines Day is an odd holiday, the feast day of a saint and a celebration of romance at the same time. It’s been evolving for a long time. While the operant word for the modern celebration is “love,” the holiday has its roots firmly in “sex.”
From Feb. 13 to 15, the Romans celebrated the feast of Lupercalia. The men sacrificed a goat and a dog, then whipped women with the hides of the animals they had just slain.
The Roman romantics "were drunk. They were naked," says Noel Lenski, a historian at the University of Colorado at Boulder. Young women would actually line up for the men to hit them, Lenski says. They believed this would make them fertile.
The brutal fete included a matchmaking lottery, in which young men drew the names of women from a jar. The couple would then be, um, coupled up for the duration of the festival — or longer, if the match was right.
The saint known as Valentine came later, and like Christmas and other holidays, the church used the feast day to supplant the earlier pagan celebration. Read how that happened, and more of the history of Valentines Day, at NPR.