Through history we learn that there were many Christians named Valentine who were martyred for their faith. St. Valentine was thought to possibly be a priest martyred during a persecution instigated by Emperor Claudius II. This happened on February 14, 270. In his honor, a basilica was dedicated in Rome in the year 350. Soon his feast day of February 14th became associated with boys and girls exchanging a promise of love. This was celebrated in different ways throughout the centuries and has evolved into our present day traditions.
How did he become associated with these traditions?
There are several legends like one that says while Valentine was in prison awaiting death for his faith he wrote a note to the daughter of his jailer, sneaking it to her and signing it with the words, "from your Valentine."
Greg Dues writes in his book, Catholic Customs & Traditions: "A more likely explanation lies in the fact that on about the same day as the annual feast of St. Valentine, there was a pagan Roman festival, Lupercalia (latin lupus, "wolf"). It celebrated the pastoral god, Lupercus (Roman equivalent to the Greek god Pan), to gain protection from wolves. This festival came under the patronage of Juno, the goddess of love. As part of the festivities, young boys and girls chose partners, proposed marriage, and became engaged, or at least picked a partner for the following year. The festival also had fertility overtones. When the Roman Empire became Christian, the traditions of this festival continued, but St. Valentine replaced the pagan goddess Juno as the patron of love."
A couple other explanations surrounding the exchanging of love notes (or valentines) include an old English belief that birds pick their mates on the date of February 14 - this was noted in the 14th century by Chaucer in Parliament of Foules:
For this was sent on Seynt Valentyne's day
Whan every foul cometh ther to choose his mate.
Another interesting fact is that commercial Valentines didnt become popular until early in the 19th century. Homemade Valentines, especially in England, had always been a tradition.
Peace in Christ,