In the early 1170s, the inhabitants of "old" Gambassi requested, and obtained, from the bishop, the construction of a new castle. The written sources of the time are quite clear: the "homines de Gambasso veteri ... fecerunt comune ... et rogaverunt eum ut faceret castrum novum de Gambasso ut tedeschi non possint eos destruere". The motivation seems to have been linked to a question of security, namely, the danger effectively constituted by the fact that the imperial army had to pass through the area in 1172. In the following decades, the written sources mention the castrum vetus and the castrum novum on several occasions, identified, significantly, at a certain point, with the toponyms Gambassi, for the new, and Gambassino, for the old. This means that the bishop’s operation did not merely concern the restructuring of the old site, but the genuine foundation of a new fortified settlement. The castrum novum was built a short distance from the older castle. The castle layout can still be easily recognized in the regular geometric shape of the four blocks of the current historic center, once enclosed within the oval of buildings marking the line of ancient walls. The weave of the building fabric, interrupted by the only free space of the current Piazza del Castello, clearly shows that the origin of "new" Gambassi was the result of a plan. The two Gambassi castles, the "new" and the "old", coexisted, facing each other, for about a century. The one, by now inadequate from a defense point of view, still remained the residence of a part of the old families of the bishop’s entourage. The other, by contrast, became the new pole of concentration for the populace now organized into a community, and a point of reference, in case of danger, for the inhabitants of the surrounding countryside as well. This is the role that the second-generation Valdelsan castle had taken on when, at the end of the 13th century, it entered to become definitively part of the Florentine contado. During the 13th century, in fact, the two fortified villages essentially became two opposing poles. The castrum vetero was still controlled by the bishop of Volterra, while the castrum novum passed under the jurisdiction of San Gimignano, a rapidly expanding town that was superimposing itself to the very detriment of its former lord, the bishop of Volterra. It is in the context of the conflict between the two that, in the last quarter of the 13th century, the "old" castle of Gambassi was definitively destroyed by San Gimignano. By that time, however, San Gimignano had already entered the orbit of the powerful city of Florence. At the end of the century, the "new" Gambassi had already been assimilated into the territory of the Florentine republic.