Before the Battle of the Milvian Bridge in Rome, Emperor Constantine reportedly saw a vision of a cross of light in the sky with the words 'In this sign, you will conquer.' Interpreting this as a divine omen from the Christian God, he ordered his soldiers to paint the Chi-Rho symbol on their shields. This event led to Constantine's victory and his subsequent conversion, which legitimized Christianity throughout the Roman Empire.

Constantine's vision became a foundational myth of Christian empire, celebrated in Eusebius's Life of Constantine and echoed in countless later religious and epic poems, from Dante's Divine Comedy to Milton's Paradise Lost. It represents the moment when a personal omen reshaped world history and became a cornerstone of Western literary and religious tradition.