Celebrated as the Holiday of Love, Valentine’s Day is the annual day of affection and appreciation, when couples, friends and families express their fondness for one another.

Its origins, however, were not so romantic. It was most probably created after St. Valentine of Terni, a third-century Christian martyr.

There are varying accounts of his stories, as well as stories of other saints also named St. Valentine. Therefore, the truth remains unclear.

The most popular, however, accounts his defiance of Roman Emperor Claudius II, who imprisoned and later executed St. Valentine. In prison, he sent letters to a woman with whom he was enamored. This woman was rumored to be his jailer’s daughter. Each letter was signed with the phrase, “From your Valentine,” a phrase still used in modern-day Valentine messages.

By the Middle Ages, he became one of the most popular saints in England and France.

He was martyred on Feb. 14, when Valentine’s day is celebrated.

Although this is the most probable reason for why the holiday is observed, another theory is that it might have been an attempt by early Catholics to Christianize the Pagan holiday of Lupercalia. Lupercalia is a Roman festival honoring Faunus, the Roman god of agriculture. However, this holiday was later outlawed in the fifth century.

Today, Valentine’s Day is among the most commercialized holiday in the U.S., third after Christmas and Halloween. Every year, more than a billion Valentine’s Day cards are sent, while $18.9 million is spent annually on Valentine’s flowers, jewelry, chocolate and cards.