Military standard of the imperial Roman legions from the time of Constantine I (c. 285-337). It featured the Christian monogram of the Greek letters Chi (X) and Rho (P), which begin the word "Christ." Constantine was Roman emperor from 306 to 337. Prior to battle with an imperial rival at the Milvian Bridge near Rome in 312, Constantine had a vision that apparently led to his conversion to Christianity. He saw a fiery cross in the heavens above the statement written in Greek, "In this sign you will conquer." According to Lactantius, Constantine had a dream telling him to place the Chi-Rho monogram on the shields of his soldiers. Slightly different accounts of this story are provided by Lactantius and Eusebius of Caesarea. After Constantine's victory at the Milvian Bridge, he and the emperor Licinius published the Edict of Milan in 313. It granted religious freedom throughout the Roman Empire. Constantine was a strong supporter of Christianity, and sought to build a Christian empire. The labarum was widely used as a Constantinian insignia. The Chi-Rho is an ancient Christian symbol that is still used as a sacred monogram today.
Glossary definitions provided courtesy of Church Publishing Incorporated, New York, NY,(All Rights reserved) from "An Episcopal Dictionary of the Church, A User Friendly Reference for Episcopalians," Don S. Armentrout and Robert Boak Slocum, editors.