In 312 AD the title of Emperor of Rome was disputed. the two main contenders were Maxentius, disputed emperor since 306 AD and Constantinus, he had imperial family ties and had been proclaimed, by his army, true emperor.

In the evening before the two armies clashed Constantinus and his army saw a cross in the sky. The cross was inscribed, In Hoc Signo Vinces ("In this Sign Thou Shalt Conquer"). Constantinus was visited by Christ in a dream that night. Christ instructed Constantinus to take the cross as his emblem. The next morning Constantinus had his troops inscribe the cross on their shields along with the Greek letters Chi and Rho.

Constantinus was victorious in the ensuing battle. When he became emperor he restored the Christian faith and became know as Constantine the Great.