Saint Valentine's Day, Western European Christian holiday, originally the Roman feast of Lupercalia. It was christianized in memory of the martyrdom of St. Valentine in A.D. 270, who, in medieval times, came to be associated with the union of lovers under conditions of duress. The holiday is celebrated on Feb. 14th by the exchange of romantic or comic verse messages called “valentines.” The first commercial valentine greeting cards produced in the United States were created in the 1840s by Esther A. Howland. Today millions of such cards are sold annually.