No sooner had spring come than the Florentine army, headed by their Podesta, Jacopino Rangoni of Modena, entered the territory of the republic and advanced upon Siena by way of Colle and Montereggioni, forcing the Sienese to raise the siege of Montemassi, and to withdraw all their troops for the defence of the city. On the morning of May 18th, there was a smart engagement at Santa Petronilla outside the Porta Camollia. A small force of Germans and Sienese made a vigorous sortie, in which the Germans bore the brunt of the fighting, lost the greater part of their number killed, and the royal banner fell into the hands of the Florentines, who retired to their encampment, having suffered severely in killed and wounded. They broke up their camp and retreated on the 20th, almost simultaneously with the return of Provenzano and his colleagues to Siena followed by a strong force of German and Italian mercenaries from the King.[6] The war was at once renewed with activity, Provenzano Salvani being the leading spirit throughout. Montemassi was taken and Montalcino rigorously blockaded. The critical condition of Montalcino combined with Ghibelline intrigues to bring the Florentines again into the field. Farinata and his fellow exiles gave the _anziani_, who then ruled in Florence, to understand that Siena was thirsting for a change of government, for the overthrow of the Twenty-four, and the banishment of Provenzano, "who was the greatest _popolano_ of Siena," and that the nobles were prepared to sell the city to the Florentines. In spite of the strenuous opposition of Tegghiaio Aldobrandino and the Conte Guidoguerra, the Florentines decided instantly to resume hostilities--nominally to relieve Montalcino, in reality to destroy Siena. They called the people to arms to follow the standards of their companies, summoned aid from Lucca and Bologna and all the Guelf cities of their league. At the beginning of September the army of Florence with the Carroccio or battle car of the Republic, over which floated the red and white standard of the Commune, entered the Sienese contado, where it was joined by the men of Perugia and Orvieto. Without counting these, there were at least 3000 horsemen and more than 30,000 infantry; but there were traitors in the army, in secret understanding with the enemy. From their camp beyond the Arbia, the captain and commissaries of the Florentines sent ambassadors to the Sienese, to demand their instant and absolute submission. "Straightway throw down your walls," they began, "in order that we may enter your city at whatever place likes us best."