Why is it call Valentine's Day? Traced back 3rd century AD, the Roman Emperor in order to avoid married men do not want be a soldier, it issued a prohibition of marriage, but Sanctus Valentinus, the bishop contrary to the emperor's will, and hold the wedding for the young people secrectly. Finally imprisoned, and died on February 14, 273. Descendants in order to commemorate him, it's became a memorial day, what we called as Valentine's day.