It’s hard to say exactly how or when Valentine’s Day first started. Some say it began as an ancient Roman festival called Lupercalia, which took place in February and included rituals to pair up young men and women. As the Roman Empire converted to Christianity, some old festivals were converted to Christian holidays. Around the year 270, a priest named Valentine secretly married couples against the emperor’s orders, and, as a result, he was jailed and died on February 14th. In honor of this priest, the Pope named February 14 as St. Valentine’s Day. In Medieval Europe, people began sending love notes on Valentine’s Day, and that’s how Valentine cards started.
Answer provided by Yahooligans.com