Many have asked me how I shall consider Christianity in the sequence of my work. In brief, I may say that I shall follow a different method from that which its historians have taken up to this time: they have studied especially how there was formed that part of Christianity which yet lives and is the soul of it, namely, the religious doctrine. On this account, they generally separate its history from the history of the Empire, making of it the principal argument, considering the history of Roman society as subordinate to it and therefore only an appendix. I propose to reverse the study, taking Christianity as a chapter, important but separate, in the history of the Empire. If for three centuries Christianity has been gradually returning to its origin, that is, becoming purely a religion and a moral teaching, for some centuries in the ancient world it was a thing much more complicated; a government and an administration that willed not only to regulate the relations between man and God, but to govern the intellectual, social, moral, political, and economic life of the people! The historian ought to explain how this new Empire--for it was indeed a new Empire--was formed in Rome and upon its ruins: this is a problem much more intricate than at first appears. It has been said and often repeated that the Church was in the Middle Ages in Europe the continuation of the Roman Empire, that the Pope is yet the real successor of the Emperor in Rome. In fact he carries one of the Emperor's titles, _Pontifex maximus_. The observation is just, but it should not make us forget that the Christian Empire, so to call it, and the Roman Empire, were between themselves as radically opposed as two forces that created the one and the other; politics and intellectuality. The diplomatists, the generals, the legislators of Rome created by political means, by wars, treaties, laws, a grand economic and political unity, which they consolidated, quite giving up the formation of a large intellectual and moral unity. The intellectual men, who formed the most powerful nucleus of the Church after the fourth century, took up again the Roman idea of unity and of empire; but they transferred it from matter to mind, from the concrete world of economic and political interests, to the world of ideas and beliefs. They tried to re-do, by pen and word, the work of the Scipios, of Lucullus, and of Cæsar, to conquer the world, not indeed invading it with armies, but spreading a new faith, creating a new morality, a new metaphysics which must gather up within themselves the intellectual activities of Græco-Latin culture, from history to science, from law to philosophy.