Afterwards, in the year 1529, when preparations were being made for the war against Florence and the siege, Pope Clement VII, wishing to study the exact site of the city and to consider in what manner and in what places his forces could be distributed to the best advantage, ordained that a plan of the city should be made secretly, with all the country for a mile around it--the hills, mountains, rivers, rocks, houses, churches, and other things, and also the squares and streets within, together with the walls and bastions surrounding it, and the other defences. The charge of all this was given to Benvenuto di Lorenzo della Volpaia, an able maker of clocks and quadrants and a very fine astrologer, but above all a most excellent master in taking ground-plans. This Benvenuto chose Tribolo as his companion, and that with great judgment, for the reason that it was Tribolo who suggested that this plan, for the better consideration of the height of the mountains, the depth of the low-lying parts, and all other particulars, should be made in relief; the doing of which was not without much labour and danger, in that, staying out all night to measure the roads and to mark the number of braccia between one place and another, and also to measure the height of the summits of the belfries and towers, drawing intersecting lines in every direction by means of the compass, and going beyond the walls to compare the height of the hills with that of the cupola, which they had marked as their centre, they did not execute such a work save after many months; but they used great diligence, for they made it of cork, for the sake of lightness, and limited the whole plan to the space of four braccia, and measured everything to scale. Having then been finished in this manner, and being made in pieces, that plan was packed up secretly and smuggled out of Florence in some bales of wool that were going to Perugia, being consigned to one who had orders to send it to the Pope, who made use of it continually during the siege of Florence, keeping it in his chamber, and seeing from one day to another, from letters and despatches, where and how the army was quartered, where skirmishes took place, and, in short, all the incidents, arguments, and discussions that occurred during that siege; all greatly to his satisfaction, for it was in truth a rare and marvellous work.