To assess the seismic vulnerability of masonry buildings is largely matter of personal feeling and experience especially when dealing with old houses made of heterogeneous materials and without a plan. One way to predict their resistance to earthquake forces is the experience on models put on a shaking table. Costs and scaling problems, particularly severe for stone walls, are limiting factors in the extensive use of this technique. After the Friuli 1976 earthquake, the regional government arranged a detailed survey of damages suffered by buildings to be repaired. These data organised in the FRED (Friuli Earthquake Database) make it possible to compare, on a statistically significant basis, the a priori vulnerability with the effective damage. One further step towards the practical use of the results is given by characterising the relevant features of the buildings with the same parameters which can be found in the General Census periodically produced by the Italian Statistical Institute (ISTAT).