Historical masonry structures are a vital part of cultural heritage but are more vulnerable to damage due to their age and material properties. This vulnerability is a concern during both natural disasters, like earthquakes, and human activities such as tunneling producing ground settlements. Therefore, there is a strong interest in developing reliable computational methods to assess the structural capacity of these buildings. This study assesses the vulnerability of "Castel Sant'Angelo", in Rome, to the effects of the tunnel excavation for Rome Line C underground. Castel Sant'Angelo is a monumental masonry building located in the Borgo district, a small area bounded by Vatican City and a bend of the Tiber River. The geometry of the monument reflects its evolution from Emperor Hadrian's 2nd century mausoleum to today's museum and comprises several structural parts: the main central structure; the outer enclosure; and the Passetto di Borgo, an arched pedestrian bridge extending westward to connect the castle with Vatican City. To evaluate the impact of ground settlements on the monument, a detailed three-dimensional numerical model [1] is developed using solid and shell finite elements. Two types of static analyses are performed [2], considering both linear elastic and nonlinear masonry behavior. In the linear analysis, potential masonry damage is assessed using the Boscardin and Cording [3] approach, which compares strains from settlements with empirically determined limit values. For the nonlinear analysis, a smeared crack model [4] is used to more accurately evaluate crack patterns in masonry. This approach simulates the cracking process and the resulting degradation under increasing stress-strain conditions caused by ground settlements. REFERENCES [1] D. Addessi, S. Marfia, E. Sacco, and J. Toti, Modeling approaches for masonry structures. The Open Civil Eng J, (2014) 8(1): 288-300. [2] D. Addessi, P. Di Re, A. Paolone. Vulnerability assessment of historical masonry buildings to excavation-induced settlements: Palazzo Assicurazioni Generali. Materials Research Proceedings (2023) 26: 355-360. [3] M.D. Boscardin and E.J. Cording, Building response to excavation-induced settlement, J Geotech Eng, (1989) 115(1): 1-21. [4] M. Jirásek, Damage and smeared crack models. In: Numerical modeling of concrete cracking, CISM International Centre for Mechanical Sciences, 532. Springer, Vienna (2011).