During the whole of 1915 neither of the two armies attempted to occupy the Marmolada massif that divided the fighters. Apart from some skirmishes between enemy patrols, who had pushed themselves up onto the Marmolada di Punta Penia at 3344m, the sector remained calm until the spring of 1916, when Austro-Hungarian units occupied a number of strongpoints facing the glacier. This move threatened the Italians on Col di Lana, so they occupied the eastern part of the Piz Serauta, fortifying themselves and installing a cableway.: From then on, both sides worked intensively to reinforce their positions and protect themselves from the elements and enemy artillery. The Austrians established their central supply point under the tongue of the glacier on the Gran Poz at 2300 meters, at the uppermost point of the cableway, and from there porters took supplies to the positions at Forcella della Marmolada , 3259, Twelve, Eleven, 2800 and slot S.: Using ecrasite first, and then brute strength, they dug numerous tunnels inside the glacier to shelter from the Italian artillery firing down on them.: The works continued throughout the winter of 1916 until the construction of what was called the city under the ice was complete. This was a network of barracks, kitchens, field hospitals, storerooms and gun emplacements under the ice connected by 12km of tunnels. :