In the 4th century, Christian belief slowly replaced the traditional Roman religion. Depictions of Roman deities gradually disappeared from Roman coins.
They were replaced by the emperor holding a standard or a labarum. The labarum, the imperial standard, displayed the Chi-Rho symbol within a wreath on top: the first two Greek letters X (chi) and P (rho) of the word CHRistos.
Over the entire face of a coin, however, the Chi-Rho appeared for the first time on coins of an emperor of the old belief – some would say, a pagan emperor. This was Magnentius, who set himself up as usurper of the Western Roman Empire in 350 AD (until 353 AD).
Although Magnentius believed in the old gods, he realized that the Christians had become too powerful a group of the population to be ignored. So he deliberately chose Christian motifs for his coin designs. This bronze coin depicts him on the obverse, while the reverse shows the Christian monogram.