The Roman priest, Valentine, defied the emperor and continued to marry young lovers, in secret.
When Valentine’s actions were discovered, Claudius ordered him killed. Valentine was arrested, drag to prision and condemned to be beaten to death with clubs – and have his head cut off. Stories tell, that Valentine had left a farewell note for the jailer’s daughter and signed it “From Your Valentine”. Another story tells, that the jailer's daugther was blind, but Valentine made her see again. Perhaps starting a twisted version of the "love is blind" cliché.
For his service marrying young lovers, Valentine was named a saint after his death.
The exact origins and history of Saint Valentine are unclear.
At least three different Valentines, all of them martyrs, are mentioned, in the Catholic Encyclopedia, under the date of the 14th of February. One was a priest in Rome, the second one was a bishop in Italy and the third Valentine was a martyr in a Roman area of Africa.
The date of Valentine’s execution - and Valentine's Day - could coincide with the Feast of Lupercalia, a pagan festival of love. In 496 AD, Pope Gelasius decided to end the Feast of Lupercalia, and he declared that the 14th of February should be celebrated as St. Valentine’s Day.