Masonry arch bridges represent the greatest portion of all the bridges in use in the Italian railway network. The typological characteristics of these structures were identified on a large stock of 380 bridges located in high seismicity areas, subdividing them into a set of homogeneous classes. Subsequently a parametrical analysis was performed for each class, in order to calculate the seismic capacity of the bridges: appropriate ranges for geometrical and mechanical parameters, i.e. span length, arch thickness, span-to-rise ratio, pier height, etc. were considered, and the limit horizontal load multiplier was calculated for each relevant collapse mechanism. Finally, envelope curves representing the seismic capacity expressed in terms of limit horizontal acceleration were derived, the input data of which are only easily detectable geometric parameters. These curves can be used for a simplified vulnerability assessment of railway masonry arch bridges, and for prioritizing further investigations and retrofit interventions.