He remained two years at Burgos, in attendance on the Spanish court, conducting himself in such a way as to acquire the esteem of Ferdinand, who presented him with a number of silver vessels of great value on his departure. This was no good school for the acquirement of political integrity. The Italians were proverbially treacherous, but Ferdinand emulated them in the arts of deception. It is related of this monarch, that when he heard that Louis XII. complained of having been twice deceived by him, he exclaimed, "The fool lies, I have tricked him above ten times."
Meanwhile the aspect of affairs changed at Florence. The French were driven from Italy, and the republic paid the penalty of the weak and disarmed neutrality which it had preserved, by being forced by the allied armies to receive back the exiled Medici. The consequence of this return was a change of government, from that of a free state, to subjection to the will of a single family. Guicciardini acted with a prudence that acquired for him the favour of the new rulers; and, on his return from Spain, was received with every suitable mark of distinction. His joy, however, on returning to his native town, was clouded by the recent death of his father.
On the event of the visit of Leo X. to Florence, attended by a numerous retinue of cardinals, Guicciardini, who had lately filled the office of magistrate, was sent, with others, to receive the pope at Cortona. Leo was so struck by him, that the next day he named him his consistorial advocate, of his own accord, without solicitation: nor did his patronage stop here; he soon after took him entirely into his service, and finding that his prudence and sagacity were equal to the good opinion he had formed of him, he made him governor of Reggio and Modena. He acquitted himself with great credit in this high office. Having been educated for the robe, instead of the career of arms, the enemies of the pope cherished the notion, that he might be surprised and frightened in his government; but his firmness and judgment disconcerted all their stratagems.
When Leo X. died, the merits of Guicciardini became yet more conspicuous. The papal power was very infirmly established in Lombardy, and the duke of Ferrara, who claimed Modena and Reggio as his own, was on the alert to take advantage of the interval of weakness caused by a delay in the election of a new pope; but Guicciardini foiled him in all his attempts. His most memorable action on this occasion was his defence of Parma. He relates it with conscious pride in his history. He had been sent by cardinal Julius de' Medici to defend Parma from an attack made by the French. Guicciardini's chief difficulty was, to inspire the citizens with resolution and martial enthusiasm. He convoked them together, distributed pikes among them, and causing the defenceless part of the town, on one side of the river, to be abandoned, made strenuous efforts to intrench the other. The enemy entered the deserted portion, and the people were eager to surrender. Guicciardini pointed out to them the fact, that the hostile forces were unprovided with artillery, and so succeeded in inspiring them with some degree of resolution: he led the attack himself, and the success that attended their sortie increasing their courage, the enemy was driven, off and the siege raised. Federigo da Bozzole, who commanded the attack, had made sure of success, and declared that he had been deceived in nothing during the expedition, except in the notion that a governor, who was not a soldier, and who had newly come to the city, should carry on the defence at his own peril, when he might have saved himself without dishonour.