While Ammanati was at Siena, where Lorenzo de’ Medici visited him, he said to the latter that, by his openly favouring the Vitelli, he had himself made it impossible for the Pope to employ the mediation of the Republic instead of the Duke of Urbino in composing the difference. The Pope also complained in a brief addressed to Florence of the assistance which had been given to Vitelli, and of his remaining in the territory of the Republic, from whence a new attempt against Città di Castello might be easily made. Lorenzo de’ Medici answered that all had been done that was compatible with the freedom and honour of the State. With Niccolò it had been agreed that he should take up his residence in the neighbourhood of Pisa, and not seek to approach Città di Castello, and his Holiness might be as much at peace respecting him as if he were in the castle of St. Angelo. ‘Be assured, Holy Father,’ he added,’that I am going to work with perfect honesty, and the intention of deserving no just reproofs nor displeasure from you. I reckon the favour of your Holiness among the greatest of my treasures, and I have no desire to lose it for the sake of Messer Niccolò or anyone else.’[205] We shall see, however, how, at the time when the breach was complete, Sixtus IV. made their behaviour in these matters a crime on the part of the Florentines, and how they could only faintly defend themselves from such reproaches. That Federigo of Montefeltro, on whom the Republic believed they could rely, joined the Pope, was a heavy blow to them. Feltrier, a man of spirit and culture, and a good master of his little state, was too weak to pursue an independent policy, and followed the lead of circumstances, while the condottiere-nature preponderated in him. He had truly served the Republic in the Colleonic war, and opposed the Pope in the Malatesta feud; he now passed to the other side. King Ferrante, who well knew the military skill of Federigo, had attached him to himself, Sixtus having aided him. During the siege of Città di Castello, on August 23, 1474, the ducal dignity was conferred on him. It did not end here; the new duke was entirely attached to the Papal interest. By the acquisition of Imola, Sixtus IV. had begun to gain a firm footing with his relations in Romagna. He now smoothed the way for a connection with one of the oldest families in the province by obtaining from Federigo the promise of the hand of his eldest daughter, Giovanna, for his nephew, the brother of Cardinal Giuliano. The importance of this connection was evident. The duke had by his recently deceased wife, Battista Sforza of Pesaro, an only son, Guidubaldo, a delicate child only two years old. If he should not survive his father, the inheritance would pass to the daughters. Guidubaldo did survive his father, but was always sickly; he died childless in the time of a second Pope belonging to the Della Rovere family, and Montefeltro and Urbino, as Sixtus IV.