Carlo Borromeo and the Jesuits during the last pontificate prepared the way for a Pope who should cement and gird that building, so that it should be capable of resisting the inroads of time and should serve as a fortress of attack on heresy.
That Pope was Michele Ghislieri, who assumed the title of Pius V.in 1566.
Before entering on the matter of his reign, it will be necessary to review the state of Rome at this moment in the epoch of transition, when the mediaeval and Renaissance phases were fast merging into the phase of the Counter-Reformation.

Old abuses which have once struck a deep root in any institution, die slowly.

It is therefore desirable to survey the position in which the Papal Sovereign of the Holy City, as constituted by the Council of Trent, held sway there.
The population of Rome was singularly fluctuating.

Being principally composed of ecclesiastics with their households and dependents; foreigners resident in the city as suitors or ambassadors; merchants, tradespeople and artists attracted by the hope of gain; it rose or fell according to the qualities of the reigning Pope, and the greater or less train of life which happened to be fashionable.

Noble families were rather conspicuous by their absence than by their presence; for those of the first rank, Colonna and Orsini, dwelt upon their fiefs, and visited the capital only as occasion served.