Serious cracks apparently due to foundation settlements can be observed on the masonry walls of Palazzo della Ragione of Milan. In order to define the main causes of present damages and to identify the actual stress field on the structure, experimental and numerical investigations were carried out. They include survey of the structure, geotechnical studies, laboratory and in situ tests on masonry, finite element simulation of the structure. A new type of large scale test was adopted to study in situ stress and deformability parameters at some locations of masonry walls. A numerical identification procedure is proposed to define foundation settlements on the basis of the measured wideness of existing cracks. -- AATA