Historical masonry structures are widespread all over Europe, and most of them are in seismic areas, such as in Italy, Greece and Portugal. Therefore, a seismic vulnerability assessment is fundamental for the preservation of the historical cultural heritage of such countries. Nowadays, many methods of analysis are available. Unfortunately, they can sometimes be costly in terms of computational burden and the results obtained are strongly influenced by the input parameters adopted. It is notorious, for instance, that FEM non-linear static analyses, especially for big and complex structures, are affected by a quite large scatter of the output. This contribution aims to present a homemade limit analysis-based method to assess the seismic vulnerability of historical masonry structures in a fast and reliable manner. The approach is based on a discretization by means of infinitely resistant hexahedron elements and quadrilateral interfaces where all dissipation occurs. The collapse load is obtained through a kinematic approach. When non-linearities are lumped on interfaces, static and kinematic problems coincide, being one the dual of the other. The first provides a failure mechanism, interfaces plastic multipliers and collapse multipliers, while with the second the internal forces acting on interfaces are retrieved. The case study adopted to benchmark the procedure proposed is a historical palace (Vittorio Emanuele II building) located in Piacenza, Italy. It is a very big masonry structure, characterized by an E-shape plan and by the presence of numerous vaults.