In the north--from the Gulf of Riga to Novo Georgievsk--Marshal von Hindenburg was in command. Under him there were four armies, each under a German general: that under Von Buelow in the extreme north; that under Von Eichhorn to the south of the former and facing the Niemen River and the fortress of Kovno; the two other armies under Von Scholtz and Von Gallwitz--the latter the farthest south--were to attack the Nareff-Bobr line between Novo Georgievsk and Lomza. The central group was under the command of Field Marshal Prince Leopold of Bavaria and was reenforced by another army under General von Woyrsch, which previous to the fall of Warsaw had been fighting more independently somewhat to the south and, a day before the fall of Warsaw, had forced the strong fortress of Ivangorod on August 4, 1915. The southern group was originally exclusively Austro-Hungarian. But during the early summer of 1915 a German army under General von Mackensen had been sent into Galicia to cooperate with the Austrian forces in freeing Przemysl and Lemberg after they had assisted in throwing back the left wing of the Russian forces then fighting in Galicia and in forcing them to relinquish their hold on the mountain passes of the Carpathians. This problem having been solved, these mixed Austro-Hungarian-German forces were rearranged and reenforced, and, under the command of Von Mackensen, were to attack the retreating Russians around Brest-Litovsk. The left wing of this group was under the command of Archduke Joseph Ferdinand. To the southeast of this entire group was another army under the Austrian General Pflanzer-Baltin, which in the early summer (1915) had driven the Russians out of the Bukowina.