The Labarum is a military standard that was used in the Roman Empire, particularly associated with the reign of Emperor Constantine the Great. It featured a Christian symbol, the Chi-Rho, which combines the letters "X" and "P" to represent Christ. The Labarum symbolized the support of Christianity in the Roman military and was a sign of divine protection. The Labarum was introduced after Constantine converted to Christianity and became a significant emblem for his armies. It marked a shift in the Roman Empire, as it embraced Christianity, leading to the eventual establishment of Christianity as the state religion.