The Emperor Constantine adopted Christianity as the official religion of the Holy Roman Empire after seeing a vision of "XP" (Chi-Rho symbol) in the sky, the first 2 Greek letters in Christ's name. Constantine adopted the symbol for his army as a means of ensuring victory against his enemies. The symbol could be found on shields and armour.
If interested: en.wikipedia.org/wiki/Chi_Rho
+ Chandalier in Greek Orthodox Church +
Happy Orthodox Easter!