Both armies, from the beginning of the conflict, began the constant work of excavating caves, tunnels, trenches, walkways, shelters and underground depots, which led to the creation of entire underground towns relatively safe from enemy fire. Monte Piana and Col di Lana were notable examples of such structures, with impressive defensive systems. Other examples can be found at the Sass de Stria with its tunnels and trenches, and Lagazuoi, more excavated than any another mountain in the Dolomites; within it, a bloody battle was fought with mines.: