Soon after midnight on May 23, 1915, the Alpini and Bersaglieri of the Italian army, supported by a few battalions of first line troops and gendarmes, crossed the mountain frontier. Soon the peaks resounded with the popping of rifle fire and the louder detonations of the Austrian mountain guns. Along the whole Trentino front that night a hundred skirmishes drove back the Austrian outpost. Only a few thousand men in all were engaged. The Italian cyclist sharpshooters advanced swiftly up the steep mountain roads until greeted by musketry fire. Then they sought shelter, pushing forward from rock to rock and from tree to tree. Often the light infantry and Alpini foot soldiers were able to skirt the enemy's posts and catch them in the rear. By May 26, 1915, all Italy was thrilled by the news that all the lower passes of the Dolomites were won and breaches made at Tonale Pass along the northwest and in the Carnic and Julian Alps along the northeast front. Among the points occupied were the Montozzo Pass, 9,585 feet high, Ponte Caffaro, running into southwestern Trentino, the ridge of Monte Baldo, extending northward fifteen miles toward Arco and Roverto in southern Trentino, some of the heights looking westward toward Trento, all the valleys in the labyrinth of the Dolomites, and several footholds in the Alps of Carinthia. The eastern army was well inside Austrian territory, its left at Caporetto on the Isonzo just under Monte Nero, its center looking down on Gorizia from the heights between Indria and the Isonzo, and its right between Cormons and Terzo. Losses on both sides were surprisingly small considering the extent of territory covered by the fighting. The Austrians, after slight resistance, withdrew into their fortresses and waited behind their guns, grimly conscious that the real struggle was still before them. Then, through the holes pierced by the mountain troops, the Italian engineers began to move forward their artillery and building emplacements and constructing trenches. Skirmishing on the mountain frontier continued until the end of May, 1915. By that time Italian forces attacking Trentino had crossed the Lessini Mountains north of Verona, captured the Austrian town of Ala on the Adige, and penetrated nearly ten miles into Austrian territory. They held high ground on the south commanding the forts of Roverto, and had begun to bring up their heavy guns against this important stronghold. Roverto is one of a number of strongly fortified places girdling Trent and commanding the converging routes to this center of the Austrian defensive. Other lesser fortresses in this girdle are Laredo on the Chiese, Levico on the Brenta, and Riva at the head of Lake Garda. Upon these the Italians closed in, and there they consolidated their positions awaiting the support of the first-line troops advancing in heavy detachments, and of their artillery.