The behaviour of historic masonry constructions under earthquake is strictly dependent on structure geometry and masonry morphology, whose precise representation influences the robustness of the seismic assessment. In this process, a crucial role is played by the structural survey. Within this framework, the paper proposes an integrated methodology for assessing the seismic safety of churches, from photogrammetric survey to collapse mechanisms analysis. As a first step, a photogrammetric survey, both aero-photogrammetric and on the ground, is carried out and a 3D model is obtained through structure from motion software. This model allows to derive geometrical details and blocks shape and arrangement, the latter obtained through both a semi-automatic edge detection technique or by CAD restitutions, based on orthophotos processing. The resulting geometry of the building is therefore imported in the Distinct Element code UDEC. Finally, the local collapse mechanisms are analysed, both in terms of failure development and capacity curve, by applying an automatic push over algorithm. The proposed integrated procedure is performed to the Romanesque Church of S. Maria Maggiore in Tuscania, Italy.