Quoted from Amerisearch:
In the third century, Roman Emperor Claudius the Goth not only commanded that the Roman gods must be worshipped, but he temporarily forbade marriage, because he believed single men made better soldiers. Legend has it that Bishop Valentine risked the Emperor's wrath by refusing to worship idols and for secretly marrying young couples. Valentine was dragged before the Prefect of Rome, who condemned him to be beaten to death with clubs and have his head cut off on February 14, 269AD. While awaiting execution, it is said he prayed for the jailers' sick daughter, who miraculously recovered. He wrote her a note and signed it, "from your Valentine." In 496 AD, Pope Gelasius designated February 14th as “Saint Valentine’s Day.”
Thus a Saint's Day on which to remember the lengths to which sacrificial love can go.
The secularized version of this Saint's Day has eliminated the example of Christ, and the faith of St. Valentine, and retained only the tradition of the clubbing to death to which all fellows can be subject if they do not please their wife and/or girlfriend(s).