Here's a sign by the door of Florence's great national library. You'll find similar signs all over the city if you look carefully. They mark an event that's etched in the memories of Florentines of a certain age, but largely forgotten by the world at large: the dreadful flood of November 4, 1966.

<img class="aligncenter size-full wp-image-6264" title="Sign" src="http://davidhewson.files.wordpress.com/2010/11/sign.jpg" alt="" width="490" height="222" />The line marks the level of the flood waters. How high was this? Take a look below.

<!--more-->Here is the sign next to a side door in the entrance.

<a href="http://davidhewson.files.wordpress.com/2010/11/door.jpg"><img class="aligncenter size-medium wp-image-6265" title="Door" src="http://davidhewson.files.wordpress.com/2010/11/door.jpg?w=225" alt="" width="225" height="300" /></a>And here is the full view of the library. The door above is on the right, inside the portico. As you can see raised quite a bit already. This was an astonishing flood, one that turned the centre of Florence into a lake nine or ten feet high in places.

<a href="http://davidhewson.files.wordpress.com/2010/11/bibiloteca.jpg"><img class="aligncenter size-large wp-image-6266" title="Library" src="http://davidhewson.files.wordpress.com/2010/11/bibiloteca.jpg?w=640" alt="" width="640" height="480" /></a>

If people think about natural disasters in Italy at all from 1966 they will probably remember the disastrous floods in Venice. These caused enormous damage and happened at the same time as the Florence flood. But in human terms the Venice catastrophe was insignificant. No one died there; thirty three people lost their lives in Florence, and thousands were left homeless.

The Venice floods led to the start of the Venice in Peril appeal to safeguard the city against future damage by the sea. The breaking of the banks of the Arno generated a more rapid and real response. Volunteers descended on the city from all over the world to help, many wading through mud and filth to rescue the many precious documents and works of art that were floating in the waters of the river. The Florentines dubbed these people 'mud angels' and still talk about them fondly today.

You can still see black and white photographs of the flood in restaurants and cafes: floating cars, streets turned into rushing rivers. The Arno's a powerful, broad river. Here it is pictured yesterday, racing over a weir upstream from the Ponte Vecchio.

<a href="http://davidhewson.files.wordpress.com/2010/11/flood.jpg"><img class="alignnone size-large wp-image-6260" title="Arno" src="http://davidhewson.files.wordpress.com/2010/11/flood.jpg?w=640" alt="" width="640" height="480" /></a>

You can see some extraordinary pictures of that terrible time on the <a href="http://www.aboutflorence.com/photos-flood-in-florence.html" target="_blank">About Florence web site</a>, <a href="http://www.florin.ms/1966flood.html" target="_blank">on this site</a> (look out for the submerged tram), and <a href="http://www.florence-flood.com/" target="_blank">read some background on a site dedicated to the flood</a>.

This is what the Arno looks like today near the Ponte Vecchio, forty four years and a few days on. The authorities assure everyone a flood on such a scale could never happen again. One can only pray they're right.

<a href="http://davidhewson.files.wordpress.com/2010/11/ponte.jpg"><img class="alignnone size-large wp-image-6258" title="Ponte Vecchio" src="http://davidhewson.files.wordpress.com/2010/11/ponte.jpg?w=640" alt="" width="640" height="480" /></a>