## 1 Introduction  
The conservation and restoration of historical masonry structures comprise a challenging field of study because of the many uncertainties that are involved in determining their material properties and composition, the structural connectivity between portions belonging to different phases of construction, complex geometrical features, geological conditions, etc. Therefore, the assessment of their structural safety is a complex process that requires a thorough multidisciplinary approach that includes, but is not limited to, historical, architectural and archaeological studies, material testing, monitoring, structural analysis and geotechnical investigation. Since historic masonry structures are particularly vulnerable to seismic loading because of their mass, uncertainties related to the load definition add to the complexity of their safety assessment in seismic areas.  
The challenge in designing appropriate structural interventions in historic buildings is that the safety of the structure must be guaranteed, while simultaneously complying with conservation principles, such as the criteria of minimum intervention, compatibility and avoiding superfluous invasive approaches. Similarly, the investigation process also needs to respect the historic character of the structure and adhere to the minimum-intervention criterion. In view of this, the use of qualitative non-destructive inspection and testing complemented by quantitative structural analysis is recommended by common standards and guidelines [1; 2]. Despite the many methods of structural analysis available [3], numerical methods based on Finite Element Analysis (FEA) have gained popularity in recent years because of increased computation capability that allows for modelling complex geometry using more realistic material models that can simulate the nonlinear behaviour of masonry. There are many examples in the literature that successfully applied this approach in the analysis of heritage sites around the world [4; 5; 6; 7; 8; 9]. In situ experimental campaigns are complementary and requisite to feed numerical models with real data from the structure and provide the means to calibrate and validate numerical models [9; 10; 11; 12; 13].  
The main objective of the paper is to demonstrate how the integration of advanced inspection and analysis tools from the outset of a historic preservation project and as part of the design process can help in the selection of interventions that are minimally invasive and respectful of the historic fabric, while concurrently upgrading the seismic performance of the structure. This paper highlights the importance of planning and coordination between all the relevant disciplines involved in the project, so that apt inspection and diagnostic tools can be used to fill in the gaps where information is missing and to design optimal and integrated structural interventions in historic structures.  
The paper first outlines the applied methodology and introduces the case study. Subsequently, the non-destructive campaign and safety assessment, consisting of both geotechnical and structural investigations, are described. The subsurface (geotechnical) studies focused on assessing the stability of the supporting soil and the analysis of the superstructure included FEA and kinematic analysis. Finally, the paper presents the design approach and the different retrofitting solutions that were considered and analysed in the pursuit of the optimal intervention in terms of safety and respect to the authenticity of the structure.