Following the German occupation of Calais, the city was divided into zones based on military interest. On 23 July 1940, the northern section was officially designated a zone interdite (restricted zone), closed off entirely to civilian access. This area contained strategic fortifications and defensive installations that the occupying forces considered vital to maintain secrecy and operational control.

To enforce this separation, the German military erected a wall along Rue Mollien, marking a clear boundary between the restricted zone and the rest of Calais. Movement across this boundary was heavily controlled. Access points such as roads and bridges were monitored around the clock by German Feldgendarmerie units and military checkpoints, effectively isolating the northern part of the city. The goal was to prevent intelligence leaks to Allied forces and to secure key military positions within the city.

The division deeply affected civilian life in Calais. Families and neighbourhoods were physically and socially split, and many residents found themselves cut off from workplaces, services, and loved ones. The presence of the wall became a visible reminder of the city’s occupation and the wider conflict.

After the war, much of the wall was demolished during the reconstruction of Calais. As the city aimed to restore unity and ensure free movement, access points were reopened and traffic between the two parts of Calais normalised. However, a portion of the original wall was preserved by the French national railway company (SNCF), which repurposed it as a safety barrier to prevent pedestrian access to nearby railway tracks.

Today, a commemorative plaque is mounted on the remaining section of the wall.