The time of St. Gregory in history bore the witness of six centuries; the time of Innocent III. of twelve; the time of Leo XIII. bears that of more than eighteen centuries to the consideration of this contrast between the natural fickleness of men and of lives of men, shown from age to age, and the persistence, on the other hand, of one idea in one line of men. The eighteen centuries already past are yet only a part of an unknown future. But to construct such a Rock amid the sea and the waves roaring in the history of the nations reveals an abiding divine power. It leaves the self-will of man untouched, yet sets up a rampart against it. The explanation attempted three hundred and fifty years ago of an imposture or an usurpation is incompatible with the clearness of an idea which is carried out persistently through so many generations. Usurpations fall rapidly. But in this one case the divine words themselves contain the idea more clearly expressed than any exposition can express it. The King delineates His kingdom as none but God can; it must also be added that He maintains it as none but God can maintain. We may return to St. Gregory's own time, and note the unbroken continuity of the Primacy from St. Peter himself. It is a period of nearly six hundred years from the day of Pentecost. Just in the middle comes the conversion of Constantine. Before it Rome is mainly a heathen city, the government of which bears above all things an everlasting enmity against any violation of the supreme pontificate annexed by the provident Augustus to the imperial power, and jealously maintained by every succeeding emperor. To suffer an infringement of that pontificate would be to lose the grasp over the hundred varieties of worship allowed by the State. Yet when Constantine acknowledged the Christian faith, the names of St. Peter and St. Paul were in full possession of the city, so far as it was Christian. They were its patron-saints. Every Christian memory rested on the tradition of St. Peter's pontifical acts, his chair, his baptismal font, his dwelling-place, his martyrdom. The impossibility of such a series of facts taking possession of a heathen city during the period antecedent to Constantine's victory over Maxentius, save as arising from St. Peter's personal action at Rome, is apparent.