Valentine's Day seems to have gotten its start as a nothing-to-do holiday with a long history of irrelevance.
There are about 14 ancient saints called Valentine, but the Catholic Church rates none of them high enough to have an official day of celebration. The General Roman Calendar issued by Church, which lists all the dates for celebrating saints, used to assign a commemoration day of February 14 to a certain "St. Valentine Priest and Martyr." However, in 1969 he was deleted, and his status hasn’t changed since.
Who was this guy?
Even when he did make the calendar, St. Valentine (Priest and Martyr) seems only to have been grandfathered in without proper qualifications. His life is a blank, a tabula rasa, a cypher, a void. Presumably, he did something priestly and martyr-like, but what that was we cannot say (nothing whatever is known about his saintly acts).
Otherwise, we can only say that he was male, that he lived a long time ago (if he ever lived at all), and that he was supposed to have been (1) born on April 16 (who knows in what year) and (2) buried somewhere along the Via Flaminia "north of Rome." And, indeed, nothing was known even in ancient times (the oldest church chronicles attest to the fact that nothing was known even then). Not a very detailed biography.
In fact, if you read the discussion on Wikipedia about St. Valentine, you'll find that it's not even certain whether there were one or two (or even possibly three) Valentines formerly commemorated on February 14. Perhaps the bar for sainthood was lower in the early days of the Church?
The Poets Take St. Valentine's Day
What is often cited as the first recorded association of Valentine's Day with romance occurs in Geoffrey Chaucer's poem Parlement of Foules (1382):
For this was on seynt Volantynys day
Whan euery bryd comyth there to chese his make.
The reference to "every bird" coming to "choose his mate" may refer only to the arrival of spring that brings with it the "birds and bees" that everyone links with love and sex. Or it may relate specifically to the date of February 14 as being, even then, devoted to love.
But some sticklers object that this pre-equinoctial date would be rather early in the year for mating birds in Merrie Olde England. These nitpickers toss another saint into the Valentine soup and say that Chaucer was, in fact, talking about May 2, then listed as the saint’s day for another of the many Valentines, Valentine of Genoa, an early bishop who died circa AD 307.
However that may be, the fact remains that between Chaucer and modern times a tradition of romance slowly rose up and entwined itself around the date of February 14. The exact history of the development of the Valentine's tradition remains obscured in an amorous haze.
But everyone seems to agree that with increasing frequency, poets linked love with that day, until, by the end of the 1700s, publishers started to find it financially rewarding to compile volumes of Valentine's Day love verses for sale to those who lacked the talent to create their own. By the early 1800s, which perhaps not coincidentally was the Romantic Era, factories were mass-producing valentines.
Enter Hallmark. End of story.
How do you celebrate Valentine's Day?