The Chi Rho is an early Christian symbol formed by superimposing the letters "Χ" (Chi) and "Ρ" (Rho), which are the first two letters of the Greek word for Christ, Χριστός. This monogram has been used since the 4th century and represents Jesus Christ in Christian art and iconography. The Chi Rho became particularly significant after the Roman Emperor Constantine adopted it as a military standard, known as the Labarum, during the Battle of Milvian Bridge in 312 AD. This event marked a turning point for Christianity, leading to its acceptance within the Roman Empire.