Love it or hate, Valentine’s Day is one of the most popular holidays in the United States. Once New Year’s Day is celebrated, stores are flooded with red and pink hearts, candy, and cards offering messages of affection and appreciation for those we love. The holiday has a long, rich – sometimes strange or ugly – history.

February has long been considered a month of romance and Valentine’s Day has elements of Christianity and ancient Roman tradition. Three different saints named Valentine or Valentinus are recognized by the Catholic Church and all of them were martyred.

One of them was a priest who served in Rome during the 3rd century. Emperor Claudius II believed that single men were better soldiers than those with wives and children, so he decreed that young men could not get married. Valentine considered the law unjust and cruel so he performed marriages in secret. When Claudius discovered what Valentine was doing he had him put to death.

Other legends tell that Valentine might have been killed while trying to help Christians flee Roman prisons where they were tortured.

One story states that Valentine was imprisoned himself and sent the first incarnation of a valentine to a young girl he loved, who was possibly the jailor’s daughter. Allegedly before his death he wrote a letter to her, signed “From your Valentine.”

Each story is unclear, but they all embody traits of sympathy, heroics, and of course, romance.

By the time of the Middle Ages, St. Valentine became the most popular saint in both England and France. Some believe that Valentine’s Day is celebrated in February because Valentine died then. Others think it happens then because the Christian church wanted to influence or “Christianize” Lupercalia, a pagan fertility festival dedicated to Faunus, the Roman god of agriculture, as well as Roman founders Romulus and Remus.

Lupercalia would begin when an order of Roman priests called the Luperci gathered around the cave where Romulus and Remus were carried to by a she-wolf when they were babies. The priests would sacrifice a goat and dog for fertility and purification, respectively. They would use strips of the goat’s hide dipped in blood to promote fertility by touching them to women and crops. Later during that day the young women would place their names in a big urn in the city, then the young men would choose a name and be paired up for the next year. This practice resulted in many marriages.

Lupercalia was deemed “un-Christian” and was outlawed at the end of the 5th century. Pope Gelasius decreed February 14 as St. Valentine’s Day, though the day was not exclusively a holiday representing love until the Middle Ages. In France and England February 14 was considered the beginning of mating season for birds, making it, in the public’s mind, a day of romance.

Valentine greetings became popular during that time period, though written Valentine’s cards weren’t used until the 1400s. The oldest Valentine on record – which is still around today – was a poem written by Charles, Duke of Orleans to his wife in 1415. He wrote it while imprisoned in the Tower of London after the Battle of Agincourt. The poem is currently at the British Library in London as part of a manuscript collection. It is believed that years later King Henry V had writer John Lydgate write a Valentine note to Catherine of Valois.

The holiday is celebrated in the United Kingdom, the U.S., France, Australia, and Canada. It became popular in Great Britain around the time of the 17th century. By the time of the mid-18th century lovers, friends, and family members were giving each other notes and tokens of affection. Then at the beginning of the 20th century printed cards became the norm once printing technology had improved. The greeting cards became extremely popular, and since postage was fairly cheap, sending valentines through the mail became popular as well.

It’s believed that Americans started exchanging handmade valentines in the early 1700s. By the 1840s, Esther A. Howland started selling the first mass produced valentines, earning Howland the moniker of “Mother of the Valentine.” Her cards were elaborate pieces with lace, ribbons, and colorful images called “scrap.”

Now about one billion valentines are sent every year, making it the second largest holiday for card sending, after Christmas.