One of the customs of the young people was name-drawing. On the eve of the
festival of Lupercalia, the names of Roman girls were written on slips of paper
 and placed into jars. Each young man drew a slip. The girl whose name was chosen was to be his sweetheart for the year.

 Legend has it that the holiday became Valentine's Day after a priest named Valentine. Valentine was a priest in Rome at the time Christianity was a new religion. The Emperor at that time, Claudius II, ordered the Roman
  soldiers NOT to marry or become engaged. Claudius believed that as married men, his soldiers would want to stay home with their families rather than fight
his wars. Valentine defied the Emperor's decree and secretly married the
young couples. He was eventually arrested, imprisoned, and put to death.

 Valentine was excuted on February 14th, the eve of the Roman holiday Lupercalia. After his death, Valentine was named a saint. As Rome became more Christian, the priests moved the spring holiday from the 15th of
      February to the 14th - Valentine's Day.
Now the holiday honored Saint Valentine instead of Lupercus.

Since those times, Saint Valentine has evolved into a character we know less 
as a historic figure and more as a collection of symbols, such as, cupids,
red roses, doves and, of course, hearts. Come February, these hearts,
the targets of Cupid's arrows and the emotional center of the anatomy 
(at least in poetic tradition), are everywhere, especially on cards. 
For those, we can thank the Victorians. Until that era, sweethearts typically
  sent handwritten notes, but advances in printing technology made possible   mass production of elaborate cards. In a repressive culture that discouraged direct expressions of love, the availability of cards set off a spree:
Sweethearts began to buy cards for each other on a scale
unprecedented for any correspondence in history.