The aim of this study was to investigate the effect of the backfill on the mechanical behavior of a multi-span masonry arch with the help of the discrete element method. After defining the geometry and identifying the mechanical properties of a one-span bridge model according to real experimental results from the literature, we extended the one-span model to a multi-span model and replaced the original backfill material with different sands and clays for investigations under live load in service loading conditions. We compared the deflections, the normal stresses in the arch and the plasticity state of the backfill under the live load. Then we also made load tests in different load cases to specify the effect of the stiffness, friction angle and cohesion of the backfill on load-bearing capacity. We found that the stiffness, the friction angle and the cohesion of the backfill largely influenced the load-bearing capacity of the structure. (C) 2009 Elsevier Ltd. All rights reserved.