It was in the early hours of November 4th, 1966, when the first alarms were raised.
The autumn storms were even heavier than usual that year. Roughly a third of Tuscany's annual rainfall had fallen on the region in the space of a few days. The River Arno was dangerously swollen and, as villages upstream began calling for help, thousands of cubic metres of water were hurtling towards Florence every second.
By the morning of November 4th, then a public holiday, engineers seeking to ease the pressure on dams in the valley released another surge of water that charged toward the city at 60 kilometres an hour.
The flood filled sewers, then cellars, then the streets and squares themselves, filling the city's narrow alleys. At their height the waters reached nearly seven metres, a level not seen since the disastrous flood of 1557.
Gas, power and water supplies were cut off and emergency generators failed.
Landslides cut off access roads in and out of the city, while part of the Arno's banks collapsed.
Florence was covered by a filthy tide of water, mud and sewage mixed with oil from central heating tanks and other debris.
It swept into homes, shops, and the museums and libraries housing some of Italy's most precious works of art – including the Uffizi Galleries, a stone's throw from the river.
Emergency services rescued some 34,000 people. Many residents had left town for the public holiday, which reduced the casualties but meant that fewer people were around to help salvage the city's treasures.
At least 35 people died in Florence and the surrounding area, according to the official estimate – swept away, drowned, hit by debris or killed by fuel explosions caused by the disaster.
#4novembre1966, 53 anni fa l'alluvione di #Firenze: i #vigilidelfuoco portarono soccorso a oltre 34.000 persone e salvarono gran parte del patrimonio artistico fiorentino #pernondimenticare #passatomaipassato pic.twitter.com/Ng28l0CbWF
— Vigili del Fuoco (@emergenzavvf) November 4, 2019
Thousands of families were left homeless and thousands of businesses devastated, many beyond repair.
Mud and upturned cars in Piazza del Carmine.
The floods damaged an estimated 14,000 works of art and as many as 4 million manuscripts, more than 1 million of them in the National Central Library alone.
Among the masterpieces injured were the Gates of Paradise from the Baptistery of St John, a wooden crucifix by early Renaissance master Cimabue from the Santa Croce Basilica, and a wooden sculpture of Mary Magdalene by Donatello, which was found smeared in sticky heating oil.
Cimabue's Crucifix, which experts have been unable to restore fully.
The city remained in chaos for days after the waters receded.
But as the river retreated, the volunteers arrived: hundreds of students and art enthusiasts determined to help the official clean-up. They were dubbed the angeli del fango, 'mud angels', and their efforts would prove crucial to helping save Florence's heritage.
Volunteers help clear the Uffizi Galleries.
A vast recovery operation began.
Works of art were carefully cleaned, dried and treated to prevent mould or insect infestations, while rare books were painstakingly washed, disinfected and dried everywhere from libraries to kilns and barns.
Meanwhile people and institutions from around the world donated their funds and expertise, 'sponsoring' the restoration of museums and churches.
Artists including Pablo Picasso auctioned off their work for the benefit of the conservation effort, while Florentine director Franco Zeffirelli made a documentary about the flood that raised millions of dollars for the city.
Half a century on, thousands of works have been restored, though many more have not.
Florence has redesigned its flood defences and taken precautions to protect its heritage, including moving some of its collections out of low-level floors near the Arno.
But experts say that severe floods could hit the city again – and if they do, they're likely to be even more devastating as the city has expanded and developed.