As Louis XII's army was continuing its way towards Rome, and he received a fresh order to join it, he took his departure the next day, leaving behind him, Vitellozzo and Gian Paolo Bagliani to prosecute the siege in his absence.
Louis XII was this time advancing upon Naples, not with the incautious ardour of Charles VIII, but, on the contrary, with that prudence and circumspection which characterised him.

Besides his alliance with Florence and Rome, he had also signed a secret treaty with Ferdinand the Catholic, who had similar pretensions, through the house of Duras, to the throne of Naples to those Louis himself had through the house of Anjou.
By this treaty the two kings were sharing their conquests beforehand: Louis would be master of Naples, of the town of Lavore and the Abruzzi, and would bear the title of King of Naples and Jerusalem; Ferdinand reserved for his own share Apulia and Calabria, with the title of Duke of these provinces; both were to receive the investiture from the pope and to hold them of him.

This partition was all the more likely to be made, in fact, because Frederic, supposing all the time that Ferdinand was his good and faithful friend, would open the gates of his towns, only to receive into his fortresses conquerors and masters instead of allies.

All this perhaps was not very loyal conduct on the part of a king who had so long desired and had just now received the surname of Catholic, but it mattered little to Louis, who profited by treasonable acts he did not have to share.
The French army, which the Duke of Valentinois had just joined, consisted of 1000 lances, 4000 Swiss, and 6000 Gascons and adventurers; further, Philip of Rabenstein was bringing by sea six Breton and Provencal vessels, and three Genoese caracks, carrying 6500 invaders.
Against this mighty host the King of Naples had only 700 men-at-arms, 600 light horse, and 6000 infantry under the command of the Colonna, whom he had taken into his pay after they were exiled by the pope from the States of the Church; but he was counting on Gonsalvo of Cordova, who was to join him at Gaeta, and to whom he had confidingly opened all his fortresses in Calabria.
But the feeling of safety inspired by Frederic's faithless ally was not destined to endure long: on their arrival at Rome, the French and Spanish ambassadors presented to the pope the treaty signed at Grenada on the 11th of November, 1500, between Louis XII and Ferdinand the Catholic, a treaty which up, to that time had been secret.

Alexander, foreseeing the probable future, had, by the death of Alfonso, loosened all the bonds that attached him to the house of Aragon, and then began by making some difficulty about it.