The Chi-Rho is an ancient Christian symbol formed by superimposing the letters "Χ" (Chi) and "Ρ" (Rho), the first two letters of the Greek word for Christ, Χριστός. This symbol is often used to represent Jesus Christ and is one of the earliest forms of Christian iconography. The Chi-Rho was popularized by the Roman Emperor Constantine the Great, who reportedly saw it in a vision before the Battle of Milvian Bridge in 312 AD. He interpreted it as a sign of divine support, leading to the symbol's adoption in Christian art and its use on banners and shields.