According to Greek writer and bishop Eusebius, the Roman emperor Constantine's army had a vision in the sky at midday accompanied by the words ἐν τούτῳ νίκα (en toútōi níka: 'in this, conquer'), sometime before the Battle of the Milvian Bridge in October 312 AD, which prompted Constantine's conversion to Christianity. In the battle on the Pons Mulvius across the Tiber at Rome, Constantine's soldiers defeated his rival Maxentius at the climax of his six year-long struggle for sole possession of the title 'Augustus' in the West, while Maxentius and his men were cast into the river as the bridge collapsed during the rout.

Detail from a Greek manuscript dated 879-883 AD and containing the homilies of Gregory of Nazianzus, now in the National Library of France.