Chi-Rho

The Chi Rho is an ancient (some say "secret") Christian symbol that was later adopted by Roman Emperor Constantine the Great as part of his military standard.

"he saw with his own eyes the trophy of a cross of light in the heavens, above the sun, and bearing the inscription, In Hoc Signo Vinces" ("In this sign thou shalt conquer")

 

Jesus appeared to the Emperor in a dream, gifting him the symbol, with the promise that all would fall before Him. Constantine was also the first of the Roman Emperors to be baptised and in so doing, ended the persecution of early Christians.

The Chi Rho (☧, English pronunciation /ˈkaɪ ˈroʊ/; also known as chrismon) superimposes the first two (capital) letters — chi and rho (ΧΡ) — of the Greek ΧΡΙΣΤΟΣ (Christos).