Fortification of the Swiss alpine region began in the 1880s, shortly after the opening of the Gotthard railway. Forts similar to those of Belgian military engineer Henri Alexis Brialmont were built at Airolo, the Oberalp Pass, Furka Pass, and Grimsel Pass, all in the Central Alps. Additional positions were constructed in the area of Saint-Maurice, using mining and tunneling techniques in the steep mountainsides of the glacial valley.