Fig.1 4 th November 1966: the Arno river overflows its embankments and floods the city at Uffizi. Florence and its floods: anatomy of an hazard M. Coli Department of Earth Science, The Florence University, Florence, Italy M. Brugioni & G. Montini The Arno river Basin Authority, Florence, Italy ABSTRACT: As well known Florence suffered in 1966 a very large flood by the Arno river. That flood inter- ested almost all the medieval city, UNESCO site since 1982, and had a very large impact on the media world- wide for the damages it produced to the cultural heritage. This study analyses the natural and anthropic factors which fostered this and the others historical floods in Florence. The study also evaluates the residual hazard for floods in Florence in respect to the prevention interventions which have been executed or are in progress. 1 INTRODUCTON November 4 th 1966 the city of Florence (Italy) suf- fered a disastrous flood by the Arno river. Almost all the Florence town and its country side were covered by up to some meters of water which caused severe damages to the outstanding cultural heritage of Florence: monuments, museums, arti- facts, libraries. This flood had a large resonance in the media and an heavy impact worldwide (Fig.1). In 1982 the medieval city of Florence, inside the third city-wall ring, was elected by UNESCO as World Heritage Site. The Romans settled Florentia in 56 B.C., since then the progressive historical city growth, espe- cially that off the medieval city occurred after the middle of the XIX, had led to a large conurbation (Fig.2) which masks the natural geomorphic fea- tures of the territory.