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Origin and history

The Y communication, originally called Communication des Têtes au Randouillet, is a double caponière fortification built southeast of Briançon, in the Hautes-Alpes. This military structure, 150 metres long and 9 wide, takes the form of a rectangular vaulted building, facing north-south. It served as a covered passage between the fort of the Three Heads (north) and the fort of the Randouillet (south), while strategically barring the valley of Fontchristiane. Its thick walls (2 to 2.25 meters) and 26 windows on the west side make it a remarkable example of bastioned defensive architecture, protected by ditches on its two facades.

Designed to connect and secure the surrounding forts, communication Y appeared as early as 1711 on the plans of engineer Tardif, then in the projects of engineer Nègre in 1721. It was built from 1724 to 1734, under the influence of Vauban's defensive principles, although Vauban died before its completion. The building incorporates hydraulic elements, such as a spring water receiving basin, and a two-level gallery at its southern end. Its roof, covered with flat tiles, completes a structure that is both functional and imposing.

Used as a military depot by the French army until 1947, the communication Y was classified as a historic monument in 1989, then listed as a UNESCO World Heritage Site in 2008, as part of the fortifications of Vauban. Major renovations, carried out between 2016 and 2020, preserved this exceptional testimony of 18th century military engineering. Today owned by the municipality of Briançon, it embodies the strategic heritage of the French Alps.

The structure is distinguished by its regular plan and its bastioned fronts, typical of the fortifications of the era. Its central passage, vaulted in the middle of the pit, is pierced with glasses on the west side and crossed perpendicularly in the middle. The materials (masonry, clay) and the precise dimensions (4.5 metres wide for the inner passage) reflect a rigorous design, adapted to the topographical constraints and defensive needs of the border region.

Historical sources, including the plans of Tardif and Nègre, underline its key role in Briançon's defensive system, a strategic city close to the Italian border. The Y communication is thus part of a wider network of fortifications designed to control access to the Alpine valleys, while illustrating the evolution of military techniques between the 17th and 18th centuries.

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