Today is Valentine's Day, a big day for greeting card and candy sales, which goes back more than 1,500 years to the Feast of St. Valentine established in the fifth century, though nobody is sure exactly which of the many martyred Valentines it is the feast day of.
The ancient Romans had a fertility festival celebrated at mid-February of every year. The festival was called Lupercalia in honor of Lupa, the wolf who was said to have suckled Romulus and Remus, who went on to found the city of Rome. Lupercalia was a pagan fertility festival celebrated with sacrifices of goats and dogs, with milk and wool and blood. Young men would cut strips from the skins of the goats then strip naked and run through the city in groups, where young women would line up to be spanked with the switches, believing it would improve their fertility. Lupercalia was still wildly popular long after the Roman Empire was officially Christian, and it's not difficult to see why the Church would have wished to have a different sort of holiday take its place.
Chaucer gets credit for establishing St. Valentine's Day as a romantic occasion, when in the 14th-century he wrote in The Parlement of Foules of a spring landscape "on seynt Valentynes day" where the goddess Nature watched as every kind of bird came before her to choose and seduce their mates.
In the early 15th century, the Duke of Orleans wrote a Valentine's poem to his faraway wife while held captive in the Tower of London. Shakespeare mentioned the sending of Valentines in Ophelia's lament in Hamlet. And hundreds of years later, with the advent of cheaper postal services and mass-produced cards, the tradition of sending lacy love notes on the holiday was enormously popular with the Victorians. In 2010, more than 1 billion cards were sent worldwide.