Early one bright afternoon, seventeen centuries ago, Constantine stood staring at the sun. According to his self-appointed biographer Eusebius, Bishop of Caesarea, who claimed to have heard the story from Constantine himself, the emperor was on campaign, when, ‘around midday, as the day was declining’ he saw a shining cross of light over the sun, with the attached text ‘By this conquer’. The understandably startled ruler slept on the matter, whereupon Christ appeared in a dream and instructed him to fashion himself a copy of the holy sign, which would protect him against his enemies. He did as he had been told, took Christian clerics as his advisers and, not long afterwards, set off for Italy to fight his rival, Maxentius. The rhetorician Lactantius, writing about twenty years before Eusebius, presented a different tale in his De mortibus persecutorum: Constantine, on the eve of his decisive battle against Maxentius in a.d. 312, at the Milvian Bridge to the north of Rome, was instructed in a dream to ‘mark the heavenly sign of God’ on his shields. Constantine's moment of epiphany, sometimes equated with his ‘conversion’, has traditionally been seen both as one of history's great turning-points and as one of its most enduring enigmas. The interpretation of Constantine's vision(s) is further complicated by an anecdote that appears in an anonymous panegyric of the emperor, delivered in a.d. 310. Having turned off from the road to visit ‘the most beautiful temple in the world’, Constantine was greeted by a remarkable sight: ‘For you saw, I believe, Constantine, your Apollo, accompanied by Victory, offering you laurel crowns, which each brought an omen of thirty years [of life or rule]’.