Rocca d'Anfo - Lago di Idro - Italy
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Wikipédia

The foundations of the Rocca d’Anfo were laid by the Republic of Venice, which governed the territory of Valsabbia from 1426 to 1797. For these works the Republic appointed Count G. Francesco Martinengo. The first step of the construction was a barrage which started from the shore of the lake and arrived to the overhanging rocks. It was composed by steps of granite between double enclosing walls. On the road leading towards Tyrol there were the quarters of the troops and the most important bastions in order to stop armed men. Another function of the buildings on the road was to collect taxes and tolls imposed on people, animals and goods passing through the passage. The double enclosing walls are still visible in the superior part of the stronghold.
As a consequence of the mutated war methods and technologies, in the Napoleonic times, a structural restoration of the territorial defensive system was necessary. Therefore, the Napoleonic engineers abandoned the Venetian structures and launched a magnificent plan of enlargement which had the hub in the northern rocky side of the mountain.
At the beginning the plan was committed to Francois Nicolas Benoit Haxo and successively to Liedot. They prepared the works by drafting a detailed cartography of the area, adapting the structures to the territorial conformation. The plan included the creation of two straight lines which led from the shore of the lake to the slopes of Mt Censo, then to the other side. The infantry and the artillery were installed between these two barriers. In order to reduce the escarpments the ground was terraced, building walls up to 10m high and connecting them to one another with stairs. The southern terrace close to the lake still has a parapet, behind which, it was possible to set all pieces of ordnance necessary to avert the hostile boats. On each terrace it was also necessary to install the cannons on the casemates in order to permit them to shoot.
The plans drawn by these engineers represent a fundamental step in the history of the cartographic methods. The edifices that were erected in as little as ten years (1802-1812) testify the effort to transform the Rocca d’Anfo into one of the most grandiose and mighty strongholds in Europe. The collapse of the Napoleonic Empire prevented the completion of the works in the medium-inferior part. The integrations of the structures were built firstly by the Austrians, and then by the Kingdom of Italy between 1860-1910