The seismic retrofitting of historical masonry buildings is a critical concern because of their cultural and architectural importance. The application of Fiber Reinforced Cementitious Matrix (FRCM) composites has gained notable attention due to their mechanical compatibility with the masonry substrate and to their effectiveness in improving the seismic capacity of masonry elements, without compromising their aesthetic value. Nevertheless, the long-term durability of such retrofitting systems represents a critical concern, especially when significant temperature variations and long-time exposure to aggressive environments are considered. In the present work, the long-term effectiveness of FRCM systems for the seismic retrofitting of historical masonry buildings is analysed with reference to a two-storey masonry structure. The attention is focused on an unreinforced masonry (URM) wall, which is an exterior part of the west side of the ancient Roman Villa at “Palazzi di Casignana” (Reggio Calabria, Italy). The FRCM reinforcements of this wall are first designed for shear and flexural strengthening, in line with the provisions of CNR-DT 215/2018. Then, the seismic performance of lime-based mortar reinforcements, with basalt (B-FRCM) and E-glass (G-FRCM) fibres, is investigated considering the effects of exposure to temperature variations, ranging from ambient conditions (e.g. 23°C) up to intense solar radiation (e.g. 80°C), as well as long-term ageing (up to 50 years) in an alkaline environment. URM walls are discretised according to the equivalent frame model proposed in the TREMURI software, considering piers and spandrels structural elements and assuming degradation of the mechanical properties of B-FRCM and G-FRCM systems resulting from experimental results available in the literature. Finally, nonlinear static analyses of the original (URM) and reinforced (RM) masonry walls are performed in order to evaluate the influence of the degradation phenomena on the effectiveness of B-FRCM and G-FRCM systems against the in-plane failure mechanisms of masonry panels