The Tower of Pisa has survived undamaged from several strong earthquakes over the last 650 years – despite its severe inclination and limited ductility. No credible explanation for this remarkable seismic performance exists to date. A re-assessment of this unique case history in light of new seismological, geological, structural, and geotechnical information will be presented, aiming to address this question. The following topics will be discussed: (1) dynamic structural identification based on recorded earthquake data; (2) geophysical site characterization using an extended two-dimensional array; (3) seismic hazard and site response analysis considering horizontal and vertical motions; and (4) soil-structure interaction (SSI) analysis calibrated using lab and field data. A substantial shift in natural period, from about 0.35 seconds to over 1 second (a threefold increase – the largest known for a structure of such height) caused by SSI, a wave parameter (1∕σ) of about 0.3, and a minor effect of vertical ground motion are identified and may explain the lack of earthquake damage on the Tower. Recommendations for future research, including the need to establish a seismic bedrock deeper than 500m, will be provided.