Labarum

The first Christian military standard, designed by Constantine from his celestial vision and dream on the eve of his victory at the Milvian Bridge (313). From 324 it was the official standard of the Roman Empire. Fashioned after legionary standards, it substituted for the old pagan symbols the form of a cross, surmounted by a jeweled wreath containing the monogram of Christ, intersecting chi (X) and rho (P), on which hung a purple banner inscribed hoc signo victor eris or a Greek or Latin variant. As a new focal point for Roman unity the monogram appeared on coins, shields, and later public buildings and churches.