This sterling silver black enamel Christian symbol on a chalice charm is really nice! It measures 22 mm tall and 12 mm wide. This symbol is not not really a symbol but a mongram. It is the oldest known monogram of Jesus Christ. It is sometimes known as a "Christogram". The chi and the rho are the first three letters of Christ (Christos) in the Greek language. The chi (c) = ch and the rho (r) = r. The chi-rho became extremely popular after Emperor Constantine adopted the symbol for his military banners after seeing a vision of it in the sky. After his vision, his military force won a decisive victory against Maxentius at the Mulvian Bridge, allowing him to march on Rome.