Thus master of new and abundant resources, he lost no time in profiting by the disputes at Florence, and immediately invested Pistoia with a thousand men-at-arms and numerous infantry; the place was strong, encompassed by a double ditch, and defended by Simone della Tosa with a sufficient garrison besides many Guelfic citizens. There was a protecting force at Prato only ten miles off and within sight of its signals, so that if the town had been well provisioned it might have withstood all Castruccio’s efforts until sickness compelled him to retreat. This chief, who had remained at Pisa to complete his preparations, joined the army on the 30th of May bringing strong reinforcements, and surrounded the town with a palisaded ditch and lines of circumvallation. Here he resolved to remain; nor did all the Florentine stratagems succeed in turning him from his purpose, not even when they collected a formidable army of twenty-six hundred men-at-arms and for three days successively defied him to battle, which he constantly pretended to accept, while he only strengthened his camp with additional trenches, fresh palisades, and wide-branching abbati. Seeing no chance of provoking him, the allies changed their position, and attacked the strongest point of his entrenchments with as little skill as success, instead of cutting off his supplies by Serravalle, which he would have been unable to prevent without a battle. Sanguineto fell sick and had moreover quarrelled with some of the confederate chiefs, so that he deemed it best to retire and make a diversion elsewhere, leaving a strong convoy at Prato ready to succour the place when a fair occasion offered. On the 28th of July, after delivering another formal challenge which Castruccio was too sagacious to accept, the confederated army drew off towards Prato and thence marched in two divisions, one by Signa and the Gusciana to threaten Lucca, the other by the left bank of the Arno, which destroyed Pontadera and carried the rampart and Fosso Arnonico by storm. This was a great canal and breastwork excavated and fortified with towers by the Pisans in 1176, both as a national bulwark and an outlet for the superfluous waters of the Arno, of which river some have supposed it to be one of the three branches mentioned by Strabo. Thus was opened all the Pisan territory; San Casciano and Sansavino soon fell and Pisa saw herself insulted at her very gates with perfect impunity. Castruccio nevertheless remained immovable; he calculated on starvation and the moral effect of seeing a superior army retire without accomplishing anything, and accordingly on the 3rd of August Pistoia surrendered to sixteen hundred men-at-arms and the usual force of infantry, in face of an army of nearly double these numbers.