With the fall of Olita, Bialystok, and Brest-Litovsk, which took place on August 25-26, 1915, and is described in more detail in another chapter, the northern group under Von Hindenburg immediately increased its activities. In Courland, south of Mitau, near Bausk, heavy fighting took place, and the Russian lines, which had held their own throughout the entire retreat of the Russian armies in Poland, began to give way. At one other point the Russians had fought back inevitable retreat with special stubbornness, and that was due west of Grodno, in the neighborhood of Augustovo, which had seen such desperate fighting during and following the Russian invasion of East Prussia. But there, too, now the Germans began to make headway and were advancing against the Niemen and the last Russian stronghold on it, Grodno. At about the same time that considerable activity developed at the utmost southern end of the line in eastern Galicia, operations of equal extent and of great importance took place at the extreme northern end, in the vicinity of Riga. On August 30, 1915, parts of Von Hindenburg's northern group, under General von Beseler, reached positions south of Friedrichstadt on the Dvina. Other troops under General von Eichhorn advanced to the northeast of Olita in the direction of Vilna, while still other forces farther south stormed the city of Lipsk, less than twenty miles west of Grodno, after having forced a crossing over the Vidra River, a tributary of the Sukelka. The fighting around Friedrichstadt continued throughout the last days of August, 1915. To the south of the Niemen the advance against the Grodno-Vilna railway continued without cessation. Whatever troops were not engaged in pursuing the retreating Russian forces were now being concentrated on the approaching attack against the last Russian fortress in Poland--Grodno. To the south of it, by August 31, 1915, they had reached Kuznitsa, on the Bialystok-Grodno railway. The investment of Grodno may be said to have begun with that day. It was then that the first reports came that heavy artillery had been brought up by the Germans and was throwing its devastating shells into the fortress from the western front. Little hope was left to the Russians for a successful resistance. For whenever these heavy guns had been brought into play before, they had blasted their way to the desired goal, no matter how strong or modern had been the defenses of steel and cement.