A specific numerical model is proposed for the in-plane dynamical analysis of a masonry monument, with particular attention to the design of interventions for seismic protection. In order to perform effective compu- tational analyses, the present model is conceived to operate at the macro-scale considering the energy dissipation capacity of the masonry material, as well as the effects of the masonry texture on the local damage mechanisms. In particular, the model was implemented according with a mechanistic point of view, in the spirit of the rigid body and spring model approach, RBSM. In the present application we describe the passage from the global three dimensional model of the Maniace Castle in Syracusae to the identification of the specific collapse mechanism that is more at risk, and that can be specifically described by means of a plane model. Then, the dynamics of a transversal cross-section of the hypostyle salon of the Castle is investigated with particular attention to the enhancement of the seismic response that can be achieved by an intervention of rebuilding and reshaping of the buttresses.