It was impossible for the Italians to attack the enemy's positions, within range of the Austrian artillery on Mount Sief, which is nearly on the same level, so the entire western margin of Col di Lana was carefully and patiently mined, an undertaking which probably took months of hard work, and several tons of high explosives were distributed in such a way as to destroy the whole side of the mountain above which the enemy was intrenched. The explosion that followed was terrific. The earth shook as if rocked by an earthquake, and the havoc wrought was so great that out of the 1,000 Austrians who held the position, only 164 survived. Of course, the Austrians launched many counterattacks against this new strong position of the Italians. But the latter had fortified it so well that all attempts of their opponents to dislodge them failed. Considerable further fighting also occurred during the second half of April, 1916, and the first half of May, 1916, in the Adamello zone, adjoining the Camonica Valley, especially in the region of the Tonale Pass. The same was true of the Tofana sector on the upper Boite. But though spectacular, the results were of comparatively small importance. CHAPTER XXXIII THE AUSTRIAN MAY DRIVE IN THE TRENTINO About May 15, 1916, the Italians were at the gates of Rovereto, less than twelve miles south of Trent and seriously threatening that city. East of Rovereto the Italian lines ran along the crest of Doss di Somme to the Monte Maggio beyond Val Terragnolo and then northward to Soglio d'Aspio. The Austrian forts of Folgaria and Lavarone compelled the Italians to follow the frontier as far as Val Sugana, where they occupied good strategical positions on Austrian territory and held Ronsegno, on the railroad between Borgo and Trent. Further north the Italians held dominating positions in front of the Austrian forts at Fabonti and Monte Cola. During the preceding months the Austrian forces along the Italian front had gradually been increased, until they now numbered about thirty-eight divisions. Of these, it was estimated that sixteen divisions, or over 300,000 men had been massed by May 15, 1916, between the Adige and Brenta Rivers. Artillery, too, in comparatively great quantity and of as heavy caliber as the country permitted, had been assembled.