Before the Battle of the Milvian Bridge outside Rome, the Roman Emperor Constantine the Great reportedly looked up at the sky and witnessed a luminous cross above the sun, accompanied by the Greek words 'En Touto Nika' (In this sign, conquer). Modern scientists speculate that this 'sign in the sky' may have been a rare solar halo phenomenon or a meteor. Constantine commanded his soldiers to paint the Christian Chi-Rho symbol on their shields, leading to his victory and the eventual legalization of Christianity across the Roman Empire.

This celestial vision was immortalized by Lactantius and Eusebius, shaping the foundational legends of Christian epic poetry for centuries. It directly inspired works such as the Old English poem 'Elene' by Cynewulf, which romanticizes the discovery of the True Cross through cosmic visions.