The Center of Resistance 21 is a mixed works (1) underground and in concrete, constructed according to the no. 200 Circular, along the channel of the Roncia torrent downstream of the Plateau of the Fontanette (2).It consists of:
The weaponry consisted of three model 14 Fiat machine guns.
After the main entrance one encounters, in the following order, the shaft of the emergency exit, the photophonic station for communication with Center 22 and, after a descending staircase, the location of the power supply group.
After passing an air-tight door, the shaft continues until it meets perpendicularly the main corridor.
If you take the branch to the right you pass another air-tight door and arrive at the water reservoir and at the staircase which go up to the well of the metal tower. At the base of the staircase there is a pair of air-tight doors which seal off the area of the reservoirs from the combat block.
Starting again from the intersection with the entrance branch, the main corridor continues with downward steps which, after having passed an air-tight door located along its length, leads to the living quarters.
From there another flight of steps, along which the ammunition dump is located, arrives at the concrete combat block. Also in this case, the living quarters are sealed off by a pair of air-tight doors.
Upon arrival at the landing of the block you find a short passage which leads to the concrete casemate which is located above the ceiling of the corridor, while a branch to the left goes up about 10 steps to the metal casemate which can be reached by means of a niche located at the upper left of the corridor. There, after a double right-angle curve, you also find the secondary exit. Near the last curve, below the opening for the close defense post, you find in the pavement a trapdoor which leads to a narrow underground shaft.
The main and secondary entrances and the metal cover of the trapdoor
have been removed.
The internal air-tight doors have been removed from their hinges and, as of the last visit (12/09/1999), were leaning against the walls near their original placement, unlike the door at the top of the steps of the south block and the door along the steps between the living quarters and the entrance block, which have been taken away along with all easily removable metal parts.
Unlike with the Maginot line, where "mixed works" indicates the presence of both artillery and infantry, we use the term here to refer to constructions which consists of both external concrete blocks and underground chambers.
After the war the French renamed Center 21 as "R40".