St Valentine's Day is the feast day of two saints named Valentine; one martyred in Rome c.270, the other the Bishop of Terni, martyred soon afterwards. The custom of sending cards to one's sweetheart on this day has nothing to do with the saints; it is probably a remnant of the Roman festival Lupercalia, held on 15 February, which included fertility rites, influenced by the belief that birds choose their mates at this time