[3] In 1883 a Séré de Rivières system fortification was begun on the massif, called the Fort du Janus.

Work continued until 1889 with a blockhouse in top of the position and a rock-cut battery in the face of the mountain, which housed four 95mm naval guns.

[5] The underground component comprised three large chambers, a cistern with a capacity of 100 cubic meters of water, a kitchen, a small magazine and a connection to the 95mm gun casemate.

[6] When the position was occupied in 1938, numerous deficiencies in heat, ventilation and optical sighting equipment were uncovered.

[7] On 19 June 1940 the ouvrage was fired upon by the 149mm guns of the Italian Fort Chaberton,[2] 600 metres (2,000 ft) higher in altitude.

[16] Janus's commanding officer altered the guns' shields to open a broader line of fire against the Col de Montgenèvre.

[17] Immediately after the war, the Briançon region was regarded as an area of medium priority for restoration and reuse by the military.

However, by 1960, with France's acquisition of nuclear weapons, the cost and effectiveness of the Maginot system was called into question.