San Paolo a Riva d'Arno is an important medieval church located in Pisa, on the south bank of the Arno river. Its existence is documented before 1032, most probably around 925: its actual configuration, however, was reached only at the end of 14th century. Structural diseases, following damages by bombing during World War II, have affected the church over the last decades; cracks in the perimeter walls and problems to the wooden frames of the roof are progressively appearing. After recent earthquakes the evolution of the statical situation has forced the authorities to close the church to the public. A comprehensive investigation on both the subsoil and the structure has been carried out with the aim of conceiving, designing and implementing suitable remedial works. Particular attention has been given to the collection of quantitative data about the foundation: layout, depth, thickness and state of conservation of the masonry. Geophysical techniques, such as electric tomography and ground penetrating radar, have been attempted with doubtful results; a special technique, consisting in small diameter holes drilled through the masonry with an instrumented drilling machine, was eventually developed. To investigate earthquake effects, a thorough analysis of local amplification of seismic action has been performed. Local seismic response of the subsoil has been analysed by different techniques applied to two different subsoil models; the results obtained evidence of significant differences among the different analyses and in comparison with the prescriptions of the Italian Seismic Code
