Scarcely was the treaty with Bologna signed than Cesare received letters from the Pope recalling him to Rome, and recommending that he should not molest the Florentines in his passage a recommendation which Alexander deemed very necessary considering the disposition towards Florence of Vitelli and Orsini. He foresaw that they would employ arguments to induce Valentinois into an enterprise of which all the cost would be his, and all the possible profit their own.
The duke would certainly have obeyed and avoided Tuscany, but that precisely as the shrewd Pope had feared Vitelli and Orsini implored him to march through Florentine territory. Vitelli, indeed, flung himself on his knees before Cesare in the vehemence of his supplications, urging that his only motive was to effect the deliverance from his unjust imprisonment of Cerbone, who had been his executed brother's chancellor. Beyond that, he swore he would make no demands upon Florence, that he would not attempt to mix himself in the affairs of the Medici, and that he would do no violence to town or country.
Thus implored, Cesare gave way. Probably he remembered the very circumstances under which Vitelli had joined his banner, and considered that he could not now oppose a request backed by a promise of so much moderation ; so on May 7 he sent his envoys to the Signory to crave leave of passage for his troops through Florentine territory.
Whilst still in the Bolognese he was sought out by Giuliano de' Medici, who begged to be allowed to accompany him, a request which Cesare instantly refused, as being contrary to that to which he had engaged himself, and he caused Giuliano to fall behind at Lojano. Nor would he so much as receive in audience Piero de' Medici, who likewise sought to join him in Siennese territory, as soon as he perceived what was toward. Yet, however much the duke protested that he had no intention to make any change in the State of Florence, there were few who believed him. Florence, weary and sorely reduced by the long struggle of the Pisan war, was an easy prey. Conscious of this, great was her anxiety and alarm at Cesare's request for passage. The Signory replied granting him the permission sought, but imposing the condition that he should keep to the country, refraining from entering any town, nor bring with him into Florentine territory Vitelli, Orsini, or any other enemy of the existing government. It happened, however, that when the Florentine ambassador reached him with this reply the duke was already over the frontier of Tuscany with the excluded condottieri in his train.
It was incumbent upon him, as a consequence, to vindicate this high handed anticipation of the unqualified Florentine permission which had not arrived. So he declared that he had been offended last year by Florence in the matter of Forli, and again this year in the matter of Faenza, both of which cities he charged the Signory with having assisted to resist him, and he announced that, to justify his intentions so far as Florence was concerned, he would explain himself at Barberino.
There, on May 12, he gave audience to the ambassador. He declared to him that he desired a good understanding with Florence, and that she should offer no hindrance to the conquest of Piombino, upon which he was now bound ; adding that since he placed no trust in the present government, which already had broken faith with him, he would require some good security for the treaty to be made. Of reinstating the Medici he said nothing ; but he demanded that some satisfaction be given Vitelli and Orsini, and, to quicken Florence in coming to a decision, he pushed forward with his army as far as Forno dei Campi almost under her very walls.
The Republic was thrown into consternation. Instantly she got together what forces she disposed of, and proceeded to fling her artillery into the Arno, to the end that she should be constrained neither to refuse it to Cesare upon his demand, nor yet to deliver it.
Macchiavelli censures the Signory's conduct of this affair as impolitic. He contends that the duke, being in great strength of arms, and Florence not armed at all, and therefore in no case to hinder his passage, it would have been wiser and the Signory would better have saved its face and dignity, had it accorded Cesare the permission to pass which he demanded, rather than have been subjected to behold him enforce that passage by weight of arms. But all that now concerned the Florentines was to be rid of an army whose presence in their territory was a constant menace. And to gain that end they were ready to give any undertakings, just as they were resolved to fulfil none.
Similarly, it chanced that Cesare was in no less a hurry to be gone ; for he had received another letter from the Pope commanding his withdrawal, and in addition, he was being plagued by Vitelli and Orsini grown restive with entreaties for permission to go into either Florence or Pistoja, where they did not lack for friends. To resist them Cesare had need of all the severity and resolution he could command; and he even went so far as to back his refusal by a threat himself to take up arms against them if they insisted.
On the 15th, at last, the treaty which amounted to an offensive and defensive alliance was signed. By the terms of this, Florence undertook to give Cesare a condotta of 300 lances for three years, to be used in Florentine service, with a stipend of 36,000 ducats yearly. How much this really meant the duke was to discover two days later, when he sent to ask the Signory to lend him some cannon for the emprise against Piombino, and to pay him the first instalment of one quarter of the yearly stipend before he left Florentine territory. The Signory replied that, by the terms of the agreement, there was no obligation for the immediate payment of the instalment, whilst in the matter of the artillery they put him off from day to day, until Cesare understood that their only aim in signing the treaty had been the immediate one of being rid of his army.
The risk Florence incurred in so playing fast and loose with such a man, particularly in a moment of such utter unfitness to resist him, is, notwithstanding the French protection enjoyed by the Signory, amazing in its reckless audacity. It was fortunate for Florence that the Pope's orders tied the duke's hands and it may be that of this the Signory had knowledge, and that it was upon such knowledge, in conjunction with France's protection, that it was presuming. Cesare took the matter in the spirit of an excellent loser, Not a hint of his chagrin and resentment did he betray; instead, he set about furnishing his needs elsewhere, sending Vitelli to Pisa with a request for artillery, a request to which Pisa very readily responded, as much on Vitelli's account as on the duke's. As for Florence, if Cesare Borgia could be terribly swift in punishing, he could also be formidably slow. If he could strike upon the instant where the opening for a blow appeared, he could also wait for months until the opening should be found. He waited now.
It would be at about this time that young Loenardo da Vinci sought employment in Cesare Borgia's service. Leonardo had been in Milan until the summer of 1500, when he repaired to Florence in quest of better fortune; but, finding little or no work to engage him there, he took the chance of the duke of Valentinois's passage to offer his service to one whose liberal patronage of the arts was become proverbial. Cesare took him into his employ as engineer and architect, leaving him in the Romagna for the present. Leonardo may have superintended the repairs of the Castle of Forli, whilst he certainly built the canal from Cesena to the Porto Cesenatico, before rejoining the duke in Rome.
On May 25 Cesare moved by the way of the valley of Cecina to try conclusions with Giacomo d'Appiano, Tyrant of Piombino, who with some Genoese and some Florentine aid, was disposed to offer resistance to the duke. The first strategic movement in this affair must be the capture of the Isle of Elba, whence aid might reach Piombino on its promontory thrusting out into the sea. For this purpose the Pope sent from Civita Vecchia six galleys, three brigantines, and two galleons under the command of Lodovico Mosca, captain of the papal navy, whilst Cesare was further reinforced by some vessels sent him from Pisa together with eight pieces of cannon. With these he made an easy capture of Elba and Pianosa. That done, he proceeded to lay siege to Piombino, which, after making a gallant resistance enduring for two months, was finally pressed to capitulate.
Long before that happened, however, Cesare had taken his departure Being awaited in Rome, he was unable to conduct the siege operations in person. So he quitted Piombino in June to join the French under d'Aubigny, bound at last upon the conquest of Naples, and claiming as their treaty with him provided Cesare's collaboration.