Stone masonry buildings, whose behaviour is known to be non-linear, is still one of the ancient and most common building typology in European historical city centres and medieval villages. Nowadays, in these historical centres, it is very difficult to analyse a building as an independent structure when, for example, neighbouring buildings share the same mid-walls. It is in this context that the necessity of studying building aggregates emerged. Moreover, the majority of these old buildings in old city centres have been designed without seismic concerns, and once overpopulated, are nowadays in need of structural rehabilitation taking into account their architectural acknowledged value. This paper approaches the seismic vulnerability assessment of a stone masonry building aggregate located in San Pio delle Camere, which was slightly affected by the 2009 L'Aquila earthquake. The structure was assessed through static non-linear numerical analysis by using the 3muri ® software. Moreover, simplified methodologies based on different vulnerability index formulations were applied to compare all these outputs obtained through distinct procedures. Globally, the activities carried out have provided a clear framework on the seismic vulnerability of the examined building aggregate, supporting the vulnerability index based methodologies for a prompt and global assessment of buildings, which can be potentially useful for the development of large scale urban strategies and widespread retrofitting interventions.