The Tavannes Tunnel was built between 1873 and 1874. It is a single tunnel, 5 meters wide and 1,196 meters long. The second tunnel, built in 1936, is the only one still in use today.
Dug shortly after the Franco-Prussian War and 1,400 meters long, this single-track railway tunnel connected Verdun to Metz. Following the annexation of the latter city, the fate of the tunnel worried the military authorities. The report of the April 22, 1881, meeting of the Fortifications Committee states: "The Tavannes Tunnel, whose western end is behind the external works of Verdun, opens onto the Woêvre plain, beyond the Tavannes Fort. It is equipped with three groups of mine furnaces, and it is important that it remain in the hands of the defense until such time as it is deemed appropriate to destroy it. It is for this purpose that it is proposed to organize its eastern head defensively." The project supports two crenellated guardhouses, measuring less than 5.5 × 3.5 m, on either side of the track, against the tunnel. These guardhouses are connected by a short gallery inside the tunnel behind an armored door pierced with four firing loopholes. Between the guardhouses, the track crosses a 5.3 m long and approximately four meter deep jump, covered by "a light bridge that will be removed in time of war." Furthermore, the presence of eight mine furnaces in the center of the tunnel is also mentioned, six on the flank and two in the sky.
The advisability of building upper floors of the guardhouses was discussed, and, as usual, money was discussed at length. A letter from Battalion Commander Lerosey of the Verdun Engineers was found in the archives, writing on February 13, 1895, to the general, president of the Technical Engineering Committee: "I have the honor to inform you that the construction of the defensive guardhouses at the eastern head of the Tavannes tunnel, including the gate and the ha-ha bridge (...) was completed (...) in 1883."
The Technical Engineering Committee, in its meeting of March 5, 1895, recommended connecting the Tavannes fort to the tunnel by a gallery 160 cm wide by 230 cm high, with a length of 375 m, descending at a gradient of 14 centimeters per meter. The discussions seem to be very close to being concluded, but the information stops there, due to a lack of knowledge of the realization of these intentions. Within the proposals, the parallel with the Montmédy gallery is often mentioned[1].