So the Empire might have remained, and so one would think it naturally would have remained, a Mediterranean thing, but for that capital experiment which has determined all future history—Julius Cæsar’s conquest of Gaul—Gaul, the mass of which lay North, Continental, exterior to the Mediterranean: Gaul which linked up with the Atlantic and the North Sea: Gaul which lived by the tides: Gaul which was to be the foundation of things to come. It was this experiment—the Roman Conquest of Gaul—and its success which opened the ancient and immemorial culture of the Mediterranean to the world. It was a revolution which for rapidity and completeness has no parallel. Something less than a hundred small Celtic States, partially civilized (but that in no degree comparable to the high life of the Mediterranean), were occupied, taught, and, as it were, “converted” into citizens of this now united Roman civilization. It was all done, so to speak, within the lifetime of a man. The link and corner-stone of Western Europe, the quadrilateral which lies between the Pyrenees and the Rhine, between the Mediterranean, the Atlantic, and the Channel, accepted civilization in a manner so final and so immediate that no historian has ever quite been able to explain the phenomenon. Gaul accepted almost at once the Roman language, the Roman food, the Roman dress, and it formed the first—and a gigantic—extension of European culture. We shall later find Gaul providing the permanent and enduring example of that culture which survived when the Roman system fell into decay. Gaul led to Britain. The Iberian Peninsula, after the hardest struggle which any territory had presented, was also incorporated. By the close of the first century after the Incarnation, when the Catholic Church had already been obscurely founded in many a city, and the turn of the world’s history had come, the Roman Empire was finally established in its entirety. By that time, from the Syrian Desert to the Atlantic, from the Sahara to the Irish Sea and to the Scotch hills, to the Rhine and the Danube, in one great ring fence, there lay a secure and unquestioned method of living incorporated as one great State. This State was to be the soil in which the seed of the Church was to be sown. As the religion of this State the Catholic Church was to develop. This State is still present, underlying our apparently complex political arrangements, as the main rocks of a country underlie the drift of the surface. Its institutions of property and of marriage; its conceptions of law; its literary roots of Rhetoric, of Poetry, of Logic, are still the stuff of Europe. The religion which it made as universal as itself is still, and perhaps more notably than ever, apparent to all. II WHAT WAS THE CHURCH IN THE ROMAN EMPIRE?