General Cadorna was now in a position to begin a direct attack upon Gorizia. He assailed the Hill of Podgora, forming the barbican of the city's system of defenses and advanced a reconnoitering force toward Mount Fortin. Meanwhile he massed 500 pieces of artillery on the heights commanding the city. But the defenses of Gorizia had been well planned, and they proved their completeness by a long resistance covering a period that brought successive reports that the fortress had fallen. All these reports proved false. South of the city the Austrian intrenchments covered a front of more than ten miles, from the Mount of San Gabriele below Plava to Mount San Michele on the Carso tableland. The trenches were built in the most modern style, of concrete more than a yard thick covered with steel armor, against which ordinary shrapnel had no more effect than so much hail, and even high-explosive shells of medium power did little damage. The Italian weapons of attack were hand grenades and short knives, in the use of which the infantry were expert. Four army corps operating under the Duke of Aosta between Gorizia and the sea were beaten back by the Austrians with heavy losses. This victory so encouraged the archduke and chief lieutenant, General Boroevics, that they decided upon a counteroffensive in force. Therefore, as soon as the Italian attack slackened, the main Austrian army advanced across the Carso Plateau. The series of battles that now followed were the first engagements of any size between the Italians and the Austro-Hungarians in the open field. They began June 22, 1915, and lasted until the close of July, with a short let-up at the end of the first week in July. The theatre included the whole Carso front, the Vipacco Valley, and the southern part of the Ternovane Forest. After his first repulse General Boroevics brought up fresh corps and renewed the attack, but in the end he was driven back to his main line with shattered forces. In the Carso tableland the Austrians had as nearly perfect a position of natural defense as a general could choose. On the east of the Isonzo plain the broken, rocky wall rises in places to 1,000 feet, seamed with gullies and ravines, and bristling with forest growth which afforded ideal cover. The action of the rain has pitted the limestone with funnel-shaped holes which form natural redoubts for machine guns; and there are larger depressions and caves where heavier pieces of artillery may be placed in excellent shelter.