The chief efforts of the invaders, however, were directed toward making an advance down the Morava Valley. Their first assault was made against the Serbian positions in the mountainous country of the Podunavlie. Gallwitz here had an exceedingly difficult task, for the ground rose in rocky, steplike formation, offering all the advantages to the defenders. But the bombardment from the heavy artillery had its effect and slowly the Germans advanced. By October 23, 1915, they had reached the southern bank of the Jesenitza, not far from Palanka and had passed Rakinatz on the road to Petrovatz on the Mlava. During this same period the German left wing, having smashed Tekia with gunfire, crossed the Danube near Orsova and succeeded in taking the heights overlooking the river. On the extreme western front the Austrians crossed the Drina at Vishegrad. Thus all the rivers forming the frontiers had passed completely into the hands of the invaders. But it had been a costly gain. By this time the Austro-German forces had lost very heavily. The Serbians also had had heavy losses, but not half so many as the enemy. It was the policy of General Putnik, the Serbian Chief of Staff, to prolong the fighting as much as possible, for during this time the transports of the Allies were disembarking troops in Saloniki, at the rate of 5,000 men a day, and there was hope that eventually they would be able to advance northward, and at least save the Serbians from the Bulgarians. This same hope had stiffened the resistance of the soldiers in every skirmish. Then came word that the Russians would relieve the pressure by attacking the Bulgarians, either through Rumania, or by landing troops in either Bourgas or Varna. And once indeed the Russian ships did bombard Varna, but without any attempt at disembarking troops. As the days passed and no help from outside came, the belief began gradually to dawn on the Serbian people that they were doomed as a nation. This feeling first manifested itself in the flight of the civil population. At first the noncombatants had merely retired with the fighting line. The first three invasions had shown that the Austrians did not always refrain from committing atrocities, especially when their armies had suffered unusually. Nor was there any reason to suppose that the Germans were any kindlier to civilians. Thus it was that hardly any of the civil population remained behind in conquered territory.