1966 flood of the Arno  The 1966 flood of the Arno () in Florence killed 101 people and damaged or destroyed millions of masterpieces of art and rare books. It is considered the worst flood in the city's history since 1557. With the combined effort of Italian and foreign volunteers alike, or "angeli del fango" ("Mud Angels"), many of these fine works have been restored. New methods in conservation were devised and restoration laboratories established. However, even decades later, much work remains to be done. Located in the Tuscany region of Central Italy, the Arno river is approximately long. It flows from the Mount Falterona hills of the Apennine Mountains to the Ligurian Sea, just west of Pisa. Lush vineyards and olive groves line the river's scenic course to the west, out to sea. Principally utilized for irrigation purposes, only of the river is used for navigation. The highest flows of the river generally occur in spring and autumn of every year, when rainfall in the Apennines is at its greatest. The intensity of the 1966 flood was further increased by both the orography of the Apennines, which contributed to the high run-off rates and river discharges, and urban development. Roads, such as the Via de Calzaiuoli, served as narrow channels for floodwaters, allowing for their greater speed and destruction within the city; bridges, on the other hand, hindered river flow where it was needed, allowing water to pour over the floodplain with great force. The flood has had a lasting impact on Florence, economically and culturally. City officials and citizens were unprepared for the storm and the widespread devastation that it caused. There were virtually no emergency measures in place, at least partially because Florence is located in an area where the frequency of flooding is relatively low. In fact, approximately 90% of the city's population were completely unaware of the imminent disaster. Residents were set to celebrate their country's World War I victory over Austria on 4 November, Armed Forces Day. In commemoration, businesses were closed and many of their employees were out of town for the public holiday. While many lives were likely spared as a result, the locked buildings greatly inhibited the salvaging of valuable materials from numerous institutions and shops, with the exception of a number of jewellery stores whose owners were warned by their nightwatchmen.  5,000 families were left homeless by the storm, and 6,000 stores were forced out of business. Approximately 600,000 tons of mud, rubble and sewage severely damaged or destroyed numerous collections of books, manuscripts and fine art.