In 1882 the Austro-Hungarian Empire and the Kingdom of Italy signed the Triple Alliance, a military pact with a defensive purpose. At the same time, both countries began to construct a fortified line of defence along their common border. Forts were placed along the entire length of the Empire’s southern border, on the passes and in the valleys. The same was done on the Italian side of the border.
At Sesto two forts were built on the two sides of the valley: the Mitterberg Fort on the north side and the Haideck Fort on the south side, linked to each other and to the other forts of the Empire’s line of defence by telephone and by optic telegraph.