On February 14th in England's medieval days it was customary to put the names of young maidens in one box and young bachelors in another. One name was pulled out of each box and the new couple exchanged gifts.
The girl became the man's "valentine" for the entire next year - a tradition that came with much responsibility. The gentleman wore the name of his valentine on his sleeve (hence the saying "wearing one's heart on one's sleeve")
He was bound by rules of chivalry and society to attend to her needs and protect her from harm for the upcoming year.
This custom often led to romance and eventual marriage, so it was not taken lightly.
In the early days of the 15th century a young French Duke was taken prisoner during the Battle of Agincourt and was held prisoner in the Tower of London for many years.
He spent much of his time writing love letters and poems to his wife - true Valentine's. The British Museum still holds about 60 of these poems among their royal papers.
It wasn't until more than 200 years later when the idea of flowers as Valentines became popular.
In the 19th century people began sending small, store-bought cards and messages to someone they admired. Most often, these cards would be anonymous, and simply said "From Your Valentine".