20th Century

After doubling during the 19th century, Florence's population was to triple in the 20th, resulting from growth in tourism, trade, financial services and industry.

During World War II the city experienced a year-long German occupation (1943–1944) and was declared an open city. The Allied soldiers who died driving the Germans from Tuscany are buried in cemeteries outside the city (Americans about nine kilometres (5.6 miles) south of the city, British and Commonwealth soldiers a few kilometres east of the centre on the right bank of the Arno). In 1944, the retreating Germans demolished the bridges along the Arno linking the district of Oltrarno to the rest of the city, making it difficult for the British troops to cross. However, at the last moment Charle Steinhauslin, at the time consulate of 26 countries in Florence, convinced the German general in Italy that the Ponte Vecchio was not to be destroyed due to its historical value.

Instead, an equally historic area of streets directly to the south of the bridge, including part of the Corridoio Vasariano, was destroyed using mines. Since then the bridges have been restored to their original forms using as many of the remaining materials as possible, but the buildings surrounding the Ponte Vecchio have been rebuilt in a style combining the old with modern design. Shortly before leaving Florence, as they knew that they would soon have to retreat, the Germans executed many freedom fighters and political opponents publicly, in streets and squares including the Piazza Santo Spirito.

At the end of World War II in Europe, in May 1945, the US Army's Information and Educational Branch was ordered to establish an overseas university campus for demobilised American service men and women in Florence, Italy. The first American University for service personnel was established in June 1945 at the School of Aeronautics in Florence, Italy. Some 7,500 soldier-students were to pass through the University during its four one-month sessions (see G. I. American Universities).

In November 1966, the Arno flooded parts of the centre, damaging many art treasures. Around the city there are tiny placards on the walls noting where the flood waters reached at their highest point.

On 25 May 2016 the BBC reported that a sinkhole, thought to have been caused by a bursting of a water pipe, opened up a 200-meter hole on the Arno river bank in Florence.