The Fortress Mitterberg dates back to 1884-89. Two years before the construction work started, the Triple Alliance between the Austro-Hungarian Empire and the Kingdom of Italy was signed. In order to strengthen this defensive alliance, numerous fortifications were built on the borders and passes, including the Monte di Mezzo Fortress on the southern slope and the Haideck Fortress on the northern slope of Sesto. The aim of the 427,000 kronor expensive complex was to close the Monte Croce Pass and to block the access to the Val Pusteria valley if necessary. The fortresses were connected by telephone and visual telegraph.
