This study on Flavia Julia Helena Augusta, mother of Constantine the Great, is divided into two parts. The purpose of the first part is to ascertain the facts of Helenas life on the basis of reliable historical sources. The second part deals with the legends concerning the discovery of the True Cross in Jerusalem by Helena. Fact and fiction, which are so often confused in the secondary literature, are carefully distinguished.The first part deals with subjects like Helenas life before the reign of Constantine, her residences in Trier and Rome, her conversion, her position at the court of Constantine, and her pilgrimage to the Holy Land. The second part investigates the origin, development and function of the legends of the discovery of the True Cross, which were developed in the 4th and 5th centuries: the Helena legend, the (Syriac) Protonike legend and the Judas Cyriacus legend. An appendix deals with the portraits of Helena.