Historians trace the origins of Valentine's Day to the ancient Roman feast of Lupercalia, which was celebrated each year between Feb. 13 and Feb. 15. During the feast, men sacrificed a dog and a goat and then used the skins to strike women who believed the whippings would make them fertile. As time went on, Christian leaders superimposed a celebration of the martyred St. Valentine on the feast.
The feast of Lupercalia also featured a tradition in which names were drawn and young men and young women paired off for the duration of the celebration. If they took to one another, they would marry soon after the feast was over.
Meanwhile, in the third century, St. Valentine ignored Roman Emperor Claudius II's ban on marriage for young men in his army. The saint presided over their marriages anyway, an act of defiance for which he was executed. However, the Catholic Church later honored him with his own holiday.
In the fifth century, Pope Gelasius I combined St. Valentine's Day with Lupercalia in hopes of quashing the pagan rituals and drawing more attention to the Church. Despite the pope's intentions, the day continued to be celebrated with romantic love in mind. William Shakespeare further romanticized Valentine's Day in "Hamlet" and "A Midsummer Night's Dream," causing it to gain traction throughout Europe.
In the Middle Ages, the exchange of cards between lovers became a tradition. This practice made its way to the New World, where factory-made cards eventually took the celebration of Valentine's Day to a mass-marketing level.