Dia de la Cruz, The Day of the Cross

Many celebrate this day, the Day of the Cross, in South America, Mexico and Spain, at the third of May. But who really knows why? What is the Background of These celebrations?I have written the knowledge about it into a song.

Helena, the mother of the Roman emperor Constantine went to the Palestine and found the cross. She brought it to Rome. Constantine turned Christinan and made Christianity the Religion of the empire. That is a feat to celebrate, isnt it? I was there at the celebrations in Granada.