The Volterran ambassadors grew weary of lying in prison, and to obtain their liberty promised to comply with the commands of the Florentines. Being set free and returned to their city, the time arrived for the new Priors to enter upon office, and among those who were drawn, was one named Giusto, a plebeian, but possessing great influence with his class, and one of those who had been imprisoned at Florence. He, being inflamed with hatred against the Florentines on account of his public as well as personal injuries, was further stimulated by Giovanni di Contugi, a man of noble family, and his colleague in office, to induce the people, by the authority of the Priors and his own influence, to withdraw their country from the power of the Florentines, and make himself prince. Prompted by these motives, Giusto took arms, rode through the city, seized the Capitano, who resided in it, on behalf of the Florentines, and with the consent of the people, became lord of Volterra. This circumstance greatly displeased the Florentines; but having just made peace with the duke, and the treaty being yet uninfringed on either side, they bethought themselves in a condition to recover the place; and that the opportunity might not be lost, they immediately appointed Rinaldo degli Albizzi and Palla Strozzi commissaries, and sent them upon the expedition. In the meantime, Giusto, who expected the Florentines would attack him, requested assistance of Lucca and Sienna. The latter refused, alleging her alliance with Florence; and Pagolo Guinigi, to regain the favor of the Florentines, which he imagined he had lost in the war with the duke and by his friendship for Filippo, not only refused assistance to Giusto, but sent his messenger prisoner to Florence.
The commissaries, to come upon the Volterrani unawares, assembled their cavalry, and having raised a good body of infantry in the Val d’Arno Inferiore, and the country about Pisa, proceeded to Volterra. Although attacked by the Florentines and abandoned by his neighbors, Giusto did not yield to fear; but, trusting to the strength of the city and the ruggedness of the country around it, prepared for his defense.