At the Milvian Bridge just outside Rome, on October 28, 312, two rival Roman Emperors fought it out: Constantine was the victor, Maxentius lost and died. Famously, in Christian history and legend, Constantine won 'in the sign of the cross', inspired by a vision recounted almost a thousand years later by Jacopo da Voragine in his famous 'Golden Legend' compendium of saints' stories. Certainly Constantine 'the Great' was the emperor whose rule established Christianity as the favoured religion of the Roman Empire.

Battle of Milvian Bridge by Giulio Romano after project by Raphael in Sala di Costantino in Vatican from flickr by Mr History
Constantine's triumph consequently features in several great works of art. Perhaps the most seen -- if not necessarily most recognized -- is in the Vatican, a fresco (above) by Giulio Romano after a project by Raphael.

Piero Triumph of Constantine at Milvian Briege Arezzo from flickr by arthistory 390
The most famous, artistically, is Piero della Francesca's painting of Constantine's victory (above) in his fresco cycle 'the legend of the true cross' in Arezzo (Tuscany), in the main apse chapel of San Francesco.
But another fresco cycle of the story or legend of the cross and the battle of the Milvian Bridge deserves more attention than it usually provokes: the huge cycle by Agnolo Gaddi which fills the walls of the central apse chapel of the great Florentine Franciscan church of Santa Croce, exemplifying the church's name and -- with its contemporary stained glass windows -- gloriously completing the vista of Santa Croce's magnificent fourteenth century nave.
But another fresco cycle of the story or legend of the cross and the battle of the Milvian Bridge deserves more attention than it usually provokes: the huge cycle by Agnolo Gaddi which fills the walls of the central apse chapel of the great Florentine Franciscan church of Santa Croce, exemplifying the church's name and -- with its contemporary stained glass windows -- gloriously completing the vista of Santa Croce's magnificent fourteenth century nave.

Dream and triumph of Constantine at Milvian Bridge by Agnolo Gaddi Capella Maggiore Santa Croce from lib-art.com
The single scene here illustrates Constantine's dream on the eve of battle, in which an angel promises victory in the sign of the cross, with the battle itself on the right.
With the entire chapel now cleaned and restored, its windows scintillating and frescoes glowing, take the time to look closely. And for those of us who cannot drop in, the web site of the Opera di Santa Croce which operates and maintains the church is at least an excellent substitute.