Known since the eleventh century, the castle of Cerreto Ciampoli was one of the main fortifications of the ancient Republic of Siena (Tuscany, Italy). The magnificent ruins, located on the top of a hill overlooking the Chianti Mountains, consist of two city walls, a door, a church, the remains of some rooms and a mighty tower lying on the ground broken up into five sections of several meters in length. The present study is focused on the analysis of the mineralogical-petrographic and chemical features of the sack and the bedding mortars of the tower, and it is aimed at understanding the exceptional qualities of these mortars that, during the collapse of the artifact, prevented the tower from shattering into smaller pieces. The tenacity of these mortars appears to be the result of the concurrence of more expedients, such as the choice of well-selected materials (hydraulic limes obtained from the local Alberese limestone, sandy aggregates from well-rinsed river sands with a high silicoclastic component) and the use of particular technical methods (i.e. hot lime technique).