Millions of cards, flowers and chocolates are given to loved ones on Valentine's Day, celebrated annually on 14 February. The day gets its name from St Valentine, but there are several conflicting stories about who the saint was – so where did the tradition come from, and why do we celebrate it?

The Catholic Church recognises at least three different saints called Valentine or similar, all of whom were martyred. One of the most popular stories is that St Valentine was a priest from Rome in the third century AD.

When Emperor Claudius banned marriage after deciding single soldiers performed better, Valentine broke the rules and arranged marriages in secret. When Claudius found out, Valentine was thrown into jail and sentenced to death. In prison, he fell in love with the jailer's daughter and sent her a note signed "from your Valentine" before he was executed on 14 February.

Some believe Valentine's Day celebrates the anniversary of Valentine's death, but other suggest the mid-February date was chosen to "Christianise" the pagan celebration of Lupercalia – a fertility festival. At the end of the 5th century, Lupercalia was eventually deemed un-Christian and the church declared 14 February as St Valentine's Day. February has long been associated with romance, a month thought to mark the beginning of the mating season for birds.

Some critics state the first recorded association of Valentine's Day with romantic love is in Parlement of Foules, written in 1382 by Geoffrey Chaucer, when the notion of courtly love flourished.

"For this was on seynt Volantynys day. Whan euerybrydcomyth there to chese his make," he wrote ("For this was on St. Valentine's Day, when every bird cometh there to choose his mate").

In 18th century England, it evolved into an occasion in which lovers expressed their affection for each other by offering flowers, sweets and chocolates and sending greeting cards. Over time, the day has become synonymous with romance and love. Hallmark first offered Valentine's Day cards in 1913 and began producing them in 1916. The day is celebrated around the world.