This sterling silver Christian symbol charm is really nice! It measures 18 mm tall and 11 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.