National Geographic has a great write-up on Valentines Day.
Rest at the site
Where did Valentine's Day come from? (Think naked Romans, paganism, and whips.) What does it cost? And why do we fall for it, year after year? Read on.
Valentine's Day History: Roman Roots
More than a Hallmark holiday, Valentine's Day, like Halloween, is rooted in pagan partying. (See "Halloween Facts: Costumes, History, Urban Legends, More.")
The lovers' holiday traces its roots to raucous annual Roman festivals where men stripped naked, grabbed goat- or dog-skin whips, and spanked young maidens in hopes of increasing their fertility, said classics professor Noel Lenski of the University of Colorado at Boulder.