Historical masonry structures, as a vital part of architectural heritage, are characterized by large masonry units with dry or poorly mortared joints. Rather than relying on strength, the stability of such structures is attained mainly from the internal structure and disposition of the units. To this extent many numerical simulations and experimental campaigns have been conducted to assess their behavior and capacity under lateral loads. Using a small tilting table, tests have been performed on masonry arches over piers by varying the internal arrangement of the piers and the shallowness of the arch itself. Numerical simulations, using an in-house code based on limit analysis involving friction, have been carried out to validate and calibrate the code. The impact of interlocking among the blocks was highlighted in terms of collapse mechanisms and multipliers and it was further shown the consequence of taking into account unit imperfections. Results showed that masonry block interlocking is of major importance and influences the collapse behavior, and the contact surface in-between the blocks plays an outstanding role on the collapse mechanisms and multiplier. Additionally, numerically and experimentally the study emphasizes the importance of well-organized piers for increased structural capacity of the entire structure. The study concludes that the capacity of historical masonry structures is primarily influenced by geometry and unit disposition rather than sheer strength.