One of man's first needs was to defend himself by building walls, watchtowers, access gates to the city to convey and control the entrance and exit of foreigners, fortresses with military functions and castles to protect the signoria who governed the city, and there are still traces of all this in Florence.
The Tower of San Niccolò stands 45 metres high on the banks of the Arno river and is the last evidence of a tower with an access door to the city of Florence before they were "decapitated". Seventy-five towers were, in fact, truncated, lowering them to discourage the struggles between factions, which were building them higher and higher as a demonstration of their power.
The top of the tower is surrounded by Guelph battlements, with a walkway beneath it, for the movement of soldiers; the external part is simple, with a few arches and windows from which you can see the Arno river.
Near the tower, a thin strip of metal on the ground indicates the position of the ancient walls, which were destroyed in the period when Florence was the capital of Italy.