It will be remembered that when the expedition into Syrmia began the bulk of the Serbian army was sent to the western frontier along the Drina, to be ready to invade Bosnia when the success of the Syrmia expedition should be assured. But so well is Bosnia wooded in this section that the Serbians had not been able to observe the concentration of troops that was going on before them across the Drina. Suddenly, on the morning of September 7, 1914, the whole frontier along the Drina, from Jarak south, became alive with Austrian soldiers. North of Loznitza the fighting took on a very bloody and deadly character. All day the battle line swayed back and forth with a succession of attacks and counterattacks. Several times the Austrians almost broke through, but in the end their whole line was driven back across the river. In the Matchva district, however, they succeeded in holding a triangular patch of swamp land, bounded by Ravjne, Tolich and Jarak. But even here they were checked along a line from Ravjne to Tolich, where both sides intrenched and came to a deadlock for the time being. Here the two opposing lines continued their trench warfare without much spectacular demonstration, but with a tremendous loss of life to both sides and an expenditure of ammunition which the Serbians could little afford. Along the line south of Loznitza the fighting was not so favorable to the Serbians. The forces stationed here had been weakened in the Syrmia expedition. And then, too, the country being extremely mountainous, they had overestimated the strength of their positions. Here, on the morning of September 8, 1914, the Austrians began a general advance, beginning at Liubovia. At first they were successfully held back, but when they came on again with greatly augmented numbers, the Serbians were finally compelled to retire to a line of hills running from Guchevo, through Jagodina and Proslop to Rozani, where they intrenched themselves and prepared to resist any further advance. The Austrians, however, continued to attack. Around Krupanie below Loznitza, the Serbians made a stubborn defense and succeeded in holding the heights of Kostainik. But their southern, or left, wing continued to be driven back. By September 11, 1914, the Austrians had advanced as far as a line drawn from Shanatz to Petska. At this critical moment, however, one of the divisions of the force that had been recalled from Syrmia arrived and the combined forces were ordered to advance against the Sokolska Mountains, whose ridges were occupied by the Austrians.