Between his departure from Milan and his arrival before Imola, where his campaign was to be inaugurated, Cesare paid a flying visit to Rome and his father, whom he had not seen for a full year. He remained three days at the Vatican, mostly closeted with the Pope's Holiness. At the end of that time he went north again to rejoin his army, which by now had been swelled by the forces that had joined it from Cesena, some Pontifical troops, and a condotta under Vitellozzo Vitelli.

The latter, who was Lord of Castello, had gone to Milan to seek justice at the hands of Louis XII against the Florentines, who had beheaded his brother Paolo deservedly, for treason in the conduct of the war against Pisa. This Vitellozzo was a valuable and experienced captain. He took service with Cesare, spurred by the hope of ultimately finding a way to avenge himself upon the Florentines, and in Cesare's train he now advanced upon Imola and Forli.

The warlike Countess Caterina Sforza-Riario had earlier been granted by her children full administration of their patrimony during their minority. To the defence of this she now addressed herself with all the resolution of her stern nature. Her life had been unfortunate, and of horrors she had touched a surfeit. Her father, Galeazzo Sforza, was murdered in Milan Cathedral by a little band of patriots ; her brother Giangaleazzo had died, of want or poison, in the Castle of Pavia, the victim of her ambitious uncle, Lodovico; her husband, Girolamo Riario, she had seen butchered and flung naked from a window of the very castle which she now defended ; Giacomo Feo, whom she had secretly married in second nuptials, was done to death in Forli, under her very eyes, by a party of insurrectionaries. Him she had terribly avenged. Getting her men at arms together, she had ridden at their head into the quarter inhabited by the murderers, and there ordered as Macchiavelli tells us the massacre of every human being that dwelt in it, women and children included, whilst she remained at hand to see it done. Thereafter she took a third husband in Giovanni di Pierfrancesco de' Medici, who died in 1498. By him this lusty woman had a son whose name was to ring through Italy as that of one of the most illustrious captains of his day Giovanni delle Bande Nere.

Such was the woman whom Sanuto has called " great souled, but a most cruel virago," who now shut herself into her castle to defy the Borgia.

She had begun by answering the Pope's Bull of attainder with the statement that, far from owing the Holy See the tribute which it claimed, the Holy See was actually in her debt, her husband, Count Girolamo Riario, having been a creditor of the Church for the provisions made by him in his office of Captain-General of the Pontifical forces. This subterfuge, however, had not weighed with Alexander, whereupon, having also been frustrated in her attempt upon the life of the Pope's Holiness, she had proceeded to measures of martial resistance. Her children and her treasures she had dispatched to Florence that they might be out of danger, retaining of the former only her son Ottaviano, a young man of some twenty years; but, for all that she kept him near her, it is plain that she did not account him worthy of being entrusted with the defence of his tyranny, for it was she, herself, the daughter of the bellicose race of Sforza, who set about the organizing of this.

Disposing of forces that were entirely inadequate to take the field against the invader, she entrenched herself in her fortress of Forli, provisioning it to withstand a protracted siege and proceeding to fortify it by throwing up outworks and causing all the gates but one to be built up.

Whilst herself engaged upon military measures she sent her son Ottaviano to Imola to exhort the Council to loyalty and the defence of the city. But his mission met with no success. Labouring against him was a mighty factor which in other future cases was to facilitate Cesare's subjection of the Romagna. The Riarii in common with so many other of the Romagna tyrants had so abused their rule, so ground the people with taxation, so offended them by violence, and provoked such deep and bitter enmity that in this hour of their need they found themselves deservedly abandoned by their subjects. The latter were become eager to try a change of rulers, in the hope of finding thus an improved condition of things; a worse, they were convinced, would be impossible.

So detested were the Riarii and so abhorred the memory they left behind them in Imola that for years afterwards the name of Cesare Borgia was blessed there as that of a minister of divine justice (" tanquam minister divina justitiae ") who had lifted from them the harsh yoke by which they had been oppressed.

And so it came to pass that, before ever Cesare had come in sight of Imola, he was met by several of its gentlemen who came to offer him the town, and he received a letter from the pedagogue Flaminio with assurances that, if it should be at all possible to them, the inhabitants would throw open the gates to him on his approach. And Flaminio proceeded to implore the duke that should he, nevertheless, be constrained to have recourse to arms to win admittance, he should not blame the citizens nor do violence to the city by putting it to pillage, assuring him that he would never have a more faithful, loving city than Imola once this should be in his power.

The duke immediately sent forward Achille Tiberti with a squadron of horse to demand the surrender of the town. And the captain of the garrison of Imola replied that he was ready to capitulate, since that was the will of the people. Three days later on November 27 Cesare rode in as conqueror.

The example of the town, however, was not followed by the citadel. Under the command of Dionigio di Naldo the latter held out, and, as the duke's army made its entrance into Imola, the castellan signified his resentment by turning his cannon upon the town itself, with such resolute purpose that many houses were set on fire and demolished. This Naldo was one of the best reputed captains of foot of his day, and he had seen much service under the Sforza ; but his experience could avail him little here.