Legend has it that before a crucial battle in 312 CE, the Roman emperor Constantine the Great dreamt he saw a cross in the sky and heard a voice say: “By his sign shalt thou conquer.” Substituting a cross for the traditional Roman eagle in the emblem of his army, Constantine defeated his rival. His victory accelerated the spread of Christianity in the Roman empire.

This painting is a preparatory sketch for one of a set of tapestries representing the history of Constantine the Great. This series now adorns the Museum’s Great Stair Hall Balcony. However, this particular sketch was not used in the series. The Philadelphia tapestry showing Christ appearing to Constantine was instead based on a different interpretation of the legend, as designed by the Italian artist Pietro da Cortona (1596–1669).