Introduction: the rise and fall of Christendom

At the beginning of the Christian era, Eusebius, bishop of Caesarea, records a story which he says he heard directly from the Emperor Constantine himself. In the middle of the day, Constantine saw a vision in the sky of a cross formed from light. In case there was any doubt about what this could mean, it had a text attached with the Greek words [could not be replicated] (by this conquer). Constantine did conquer: he adopted the Chi Rho sign as his personal trophy, tolerated Christianity throughout the empire, and called the first major ecumenical council of the Christian Church, the Council of Nicaea (325), in order to make authoritative rulings on the threat posed by rival Christianities, including Arianism. From this point, Christianity steadily advanced so that it became the defining cultural feature of western Europe, surviving and thriving when the Roman Empire fell, and when all its successors, from the early medieval empire of Charlemagne to the British Empire-the greatest empire the world has ever seen-went the same way