The object of the paper is the influence the soil-structure interaction on the dynamical response of a masonry tower, for which a high level of stress is involved already in the static field. The relevant deformations and displacements at the base of the tower suggest that a significant volume of ground is engaged into the overall dynamic response, both as a participating mass and as a potential carrier of energy dissipation. In order to investigate this aspect and assess the sensitivity of the dynamic response of the soil-structure system to different soil characteristics, the non linear dynamic response of a case study is analyzed, by including in the model a significant volume of foundation soil and considering two different ground types. The numerical model is based on a specific Rigid Body and Springs approach, able to model the significant inelastic aspects of the constitutive behaviour and the meso-scale damage mechanisms with a moderate computational effort.