This paper presents the case study of the effect on the foundation of changing the structural system of a bridge from a plain concrete multi-arch bridge to a slab and girder one. The bridge was built in 1940 over the Cardener river and was designed according to a typology commonly used in that period: plain concrete ribbed arches without centering, with three arches spanning 11.5, 26.5 and 11.5 m. Piles that supported piers between arches were designed to balance the excess of horizontal force induced by the thrust of the main arch. In 1965, arches were substituted by a deck of precast girders with cast-in-situ slab. The forces and the barycenter of the vertical forces on the foundation changed in a radical way. Some of the piles resulted overstressed and other, almost completely discharged. Repair intervention was designed to assure good behavior and durability of the foundation.