As we celebrate Valentine's Day, do we know how and why it all began?

It's renowned for being the 'most romantic day of the year'.

And many of us use it as an opportunity to show affection for our loved ones with cards, flowers or chocolates.

But why exactly do we celebrate Valentine's Day and why does it fall on February 14?

Well we've trawled through the history books to find out the real reasons so you don't have to - and the background casts a very different light on the holiday.

How did Valentine's Day begin?

Valentine's Day is an old tradition thought to have originated from a Roman Festival known as Lupercalia, according to History.com.

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.

Who was St Valentine?

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The St Valentine that inspired the holiday may have been more than one man.

The saint officially recognised by the Roman Catholic Church was a real person who died around AD 270.

An account from 1400s 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.

St. Valentine the international man of mystery

He may also have been Bishop of Terni, also martyred by Claudius II on the outskirts of Rome. There are similarities between the priest's and bishop's stories, which leads people to believe they are the same man.

There's so much confusion around St Valentine that the Church stopped veneration of him in 1969 - though he is still listed as an official saint.

“Valentinus” is from the Latin word for worthy, strong or powerful, and was a popular name between the second and eighth centuries AD meaning there are several martyrs with the same name. There are actually a dozen Valentines listed and there's even a Pope Valentine. The actual day we celebrate is known as St Valentine of Rome to set him apart.

What does he really have to do with love?

Valentine did help marry couples in secret, which is arguably very romantic. He is the patron saint of beekeepers and epilepsy among other things..like the plague, fainting and travelling. That doesn't stop people calling on his help for those romantically involved. He's now also patron of engaged couples and happy marriages.

Why is his skull kept in Rome?

Yes, that's right. St Valentine's skull is housed and adorned in flowers in Rome. It's actually on display in the Basilica of Santa Maria in Cosmedin.

It was found when people were excavating a catacomb near Rome in the early 1800s. The skeletal remains and other relics now associated with St Valentine were dug up. It's the norm for these to be split and distributed to reliquaries - places that keep relics - around the world. If you wanted to see other parts of the saint, he's on display in the Czech Republic, Ireland, Scotland, England and France.

Why do we give Valentine's cards?

Another idea is that when he was sent to prison, he sent a letter to a young girl he had fallen in love with and signed it "From your Valentine".

It's thought this was the first ever Valentine's Day greeting.