It was held on February 15 as a fertility festival dedicated to Faunus, the Roman god of agriculture.
During the celebrations boys would draw names of girls from a box and the pair would be partners during the festival.
These matches often led to marriage.
The festival survived the initial rise of Christianity but was outlawed at the end of the 5th century, when Pope Gelasius declared February 14 St Valentine's Day.
Chaucer, as in The Canterbury Tales writer, may have actually been behind Valentine's Day. The medieval English poet took quite a few liberties with history. He'd drop his poetic characters into real-life historical events leaving readers wondering if that's what really happened.
There is no actual record of Valentine's Day before Chaucer's poem in 1375. It's in Parliament of Foules that he links the tradition of courtly love to the St Valentine's feast day - the tradition didn't exist until after his poem.
The poem refers to February 14 as the day of birds coming together to find a mate. “For this was sent on Seynt Valentyne’s day / Whan every foul cometh ther to choose his mate,” he wrote and maybe invented Valentine's Day as we now know it.
The Saint Valentine that inspired the holiday may have been more than one man.
The saint officially recognized by the Roman Catholic Church was a real person who died around AD 270.
An account from 1400's describes Valentine as a priest who was beheaded by Emperor Claudius II for helping Christian couples wed.
The emperor had banned marriage as he thought single men made better soldiers. Valentine felt this was unfair, so he celebrated marriages in secret. When the emperor found out, he was thrown in jail and sentenced to death.
Valentine did help marry couples in secret, which is arguably very romantic. He is the patron saint of beekeepers and epilepsy among other things... things like the plague, fainting and travelling. That doesn't stop people calling on his help for those romantically involved. He's now also the patron of engaged couples and happy marriages. What could be more romantic that that? So, Happy Valentine's Day!