The “Torre Grossa” (literally big tower) is the most relevant within the 13 towers which, nowadays, characterize the skyline of San Gimignano, the famous small town close to Siena. An extensive study on the tower has been performed within the framework of the research contract called “San Gimignano Project”. Research involved local Authorities (Municipality of San Gimignano, Tuscany Regional Administration) and four Departments of different Tuscany Universities (see Bartoli and Mennucci 2000). Even if all the towers have been studied in past years under several different points of view (mainly for architectural and archaeological investigation), no studies were performed in or¬der to check the “safety” of the monument under a structural point of view. ....