In Rome in C.E. 270, Valentine had enraged the mad emperor Claudius II, who had issued an edict forbidding marriage. Claudius felt that married men made poor soldiers, because they would not want to leave their families for battle. The empire needed soldiers, so Claudius abolished marriage.
Valentine, bishop of Interamna, invited young couples to come to him in secret, where he joined them in the sacrament of matrimony. Claudius learned of this "friend of lovers," and had the bishop brought to the palace. The emperor, impressed with the young priest's dignity and conviction, attempted to convert him to the roman gods, to save him from certain execution. Valentine refused to renounce Christianity and boldly attempted to convert the emperor. On February 24, 270, Valentine was executed.
History also claims that while Valentine was in prison awaiting his fate, he fell in love with the blind daughter of the jailer, Asterius. Through his faith he miraculously restored her sight. He then signed a farewell message to her "From Your Valentine," a phrase that would live long after its author.
Valentine was clubbed to death, then beheaded, on February 14 around 270 C.E. during the Christian persecution. In a way, it could be said he died for love, and it may be for this that his feast day, named in 496 C.E. by Pope Gelasius, has become associated with romance.
So in our empire, make love, not war, this Monday!