Meanwhile Vitellozzo Vitelli, who had assumed the title of General of the Church, and had under him 800 men-at-arms and 3,000 infantry, was following the secret instructions that he had received from Caesar by word of mouth, and was carrying forward that system of invasion which was to encircle Florence in a network of iron, and in the end make her defence an impossibility.  A worthy pupil of his master, in whose school he had learned to use in turn the cunning of a fox and the strength of a lion, he had established an understanding between himself and certain young gentlemen of Arezzo to get that town delivered into his hands.  But the plot had been discovered by Guglielma dei Pazzi, commissary of the Florentine Republic, and he had arrested two of the conspirators, whereupon the others, who were much more numerous than was supposed; had instantly dispersed about the town summoning the citizens to arms.  All the republican faction, who saw in any sort of revolution the means of subjugating Florence, joined their party, set the captives at liberty, and seized Guglielmo; then proclaiming the establishment of the ancient constitution, they besieged the citadel, whither Cosimo dei Pazzi, Bishop of Arezzo, the son of Guglielmo, had fled for refuge; he, finding himself invested on every side, sent a messenger in hot haste to Florence to ask for help.

Unfortunately for the cardinal, Vitellozzo’s troops were nearer to the besiegers than were the soldiers of the most serene republic to the besieged, and instead of help—­the whole army of the enemy came down upon him.  This army was under the command of Vitellozzo, of Gian Paolo Baglioni, and of Fabio Orsino, and with them were the two Medici, ever ready to go wherever there was a league against Florence, and ever ready at the command of Borgia, on any conditions whatever, to re-enter the town whence they had been banished.  The next day more help in the form of money and artillery arrived, sent by Pandolfo Petrucci, and on the 18th of June the citadel of Arezzo, which had received no news from Florence, was obliged to surrender.

Vitellozzo left the men of Arezzo to look after their town themselves, leaving also Fabio Orsina to garrison the citadel with a thousand men.  Then, profiting by the terror that had been spread throughout all this part of Italy by the successive captures of the duchy of Urbino, of Camerino, and of Arezzo, he marched upon Monte San Severino, Castiglione, Aretino, Cortone, and the other towns of the valley of Chiana, which submitted one after the other almost without a struggle.  When he was only ten or twelve leagues from Florence, and dared not an his own account attempt anything against her, he made known the state of affairs to the Duke of Valentinois.  He, fancying the hour had came at last far striking the blow so long delayed, started off at once to deliver his answer in person to his faithful lieutenants.