She is said to have discovered the resting place of the three crosses used at the crucifixion of Jesus and the two thieves - Dismas and Gestas - who were executed with him . Through a miracle it was revealed which of the three was the True Cross . It was afterwards claimed , in the later fourth-century history by Gelasius of Caesarea followed by Rufinus ' additions to Eusebius ' Ecclesiastical History , that she discovered the hiding place of three crosses , believed to be used at the crucifixion of Jesus and the two thieves â '' St. Dismas and Gestas â '' who were executed with him , and that through a miracle it was revealed which of the three was the True Cross .