According to MSN: "Most historians link the lover's holiday to an annual celebration in Rome that occurred every Feb. 15. During the boisterous bonanza, men stripped naked and spanked young maidens with animal-skin whips in an effort to increase fertility. While tame in comparison, modern Valentine's Day festivities are observed today in Mexico, Canada, France, Australia and the U.K., in addition to here in the U.S."
Furthermore: "While history buffs don't unanimously agree on who the original Valentine was, the most popular suspect is a clergyman in ancient Rome. When the emperor outlawed marriage during wartime (because he believed single men made better soldiers), Bishop Valentine performed secret wedding ceremonies. It wasn't until 496 A.D., over 200 years after the bishop's death, that Pope Gelasius I officially declared Feb. 14 as Saint Valentine's Day."