Chi and Rho are the first two letters (ΧΡ) of "Christ" in Greek ΧΡΙΣΤΟΣ. (Christos). Sometimes it is called the Monogram of Christ or Chrismon or Labarum.The Chi-Rho is often shown with the Greek letters Alpha (A) and Omega (lower case ώ or upper case Ω), the first and last letters of the Greek alphabet. Jesus refers to himself: "I am the Alpha and the Omega, the First and the Last, the Beginning and the End." (Revelation 22:13).The story goes that in In 312 AD, Constantine (ruled 306 - 337) was about to lead his army in a battle with his enemy Maxentius at the Milvian Bridge outside Rome. The winner would become emperor of the whole empire. Oiginally Constantine had been a pagan, but he was worried about the coming battle. He says he started to pray to the "Supreme God" for help.There was a sign in the sky "above the sun" and with it the words "conquer by this". That night in a dream he said he saw Jesus telling him to use the chi-rho sign "as a safeguard in all battles". Constantine ordered it to be put on his soldier's shields -- and won the battle.~Chi Rho, Chrismon, Monogram of Christ, Labarum by Dr. Ralph F. Wilson~