Entrance to the Frejus railway tunnel: visits not permitted but can be seen from the Autostrada del Frejus near the tunnel, and from the road between Bardonecchia and Rochemolles.
After the opening of the Frejus railway line in 1871, it was decided that defence for the tunnel itself was needed, in the event of a French strike. For this reason, the straight branch of the abandoned end tunnel was set up to house a battery, which could be pulled directly into the tunnel if needed. Work began in 1875 on the construction of the internal battery, which was equipped with an 87 mm cannon and an 86 model machine gun. A tunnel to be used by riflemen for close-range defence was added to the side of the installation, leading to a mine chamber that was capable of blowing up the tunnel if needed. A defence barracks to protect the railway entrance was found outside the straight tunnel, laid out across two floors and guarded by ditches and walls equipped with embrasures.
