The rise of Christianity up to the victory of Constantine has often been studied and remains a puzzling phenomenon. In this valedictory lecture Jan N. Bremmer concentrates on the explanations adduced, focusing in particular on the works of three iconic figures from the last two hundred and fifty years: The History of the Decline and Fall of the Roman Empire of Edward Gibbon, the most famous ancient historian of all time, at the end of the eighteenth century; Die Mission und Ausbreitung des Christentums of Adolf von Harnack, the greatest historian of early Christianity of all time, around...