He was the son of Flavius Constantius Chlorus, a Roman army officer who was one of the four emperors of the Tetrarchy. His mother, Helena, was a Greek of low social standing from Helenopolis. It is uncertain whether she was Constantius' legitimate wife or merely his concubine. In 288 or 289, Constantius left Helena to marry Emperor Maximian's stepdaughter, Theodora.
Helena, the mother of Constantine the Great, is a saint of the Catholic Church. Probably influenced by her son, she was baptized and undertook activities that resulted in the numerous basilicas she founded, including the Basilica of the Nativity in Bethlehem, the Church of the Holy Sepulchre, and the Chapel of the Ascension.
She made pilgrimages to Palestine and other eastern provinces and became famous for her generosity to the poor. Helena influenced her son to pass special laws guaranteeing state care for widows, orphans, abandoned children, prisoners and slaves. Tradition credits her with finding the relics of the Cross of the Lord.