By 11th October the Austro-Germans held a hundred miles of front on the south banks of the Save and the Danube. The Serbians had fought desperately, but they could not stand before the mass of artillery brought against them. The Serbian left had been forced back towards the hills on which it had made its first stand against the third Austrian invasion, the centre had fallen back to a ridge seven miles south of the capital, and the right was being harried across the river plain and up the valleys of the Morava and the Mlava. On the Serbian right Mackensen moved his big guns slowly. He was waiting for the Bulgarians to take the Serbians in flank and in rear. On the 12th the Bulgarians attacked the Serbians at five different points, and it was clear that, if the Serbians were to avoid being completely surrounded, they must retreat, as the Russians had done. But, unlike the Russians, they had no vast land into which they could retire. Their only line of withdrawal lay to the west and south-west, into the bare, rugged highlands of Montenegro and the wilderness of Albania. The French and British in the south were by this time struggling northwards in the attempt to reach Uskub, the great meeting-place of all routes in Southern Serbia. They were, however, too late: the Bulgarians entered Uskub on 22nd October, and the Allies were thus cut off from all communication with the interior. The Serbians were now in a desperate plight. Along every road and track left open to the south-west thousands of old men, women, and children trudged wearily onward, bearing with them the few household goods which they could carry off. Food was scarce, carts could not be obtained for love or money, and on the desolate hills thousands of wretched peasants perished of cold and hunger. By 26th October the whole north-east corner of Serbia was in the hands of the enemy. The Serbian army which lay between the Drina and Nish was cut off from that which lay in the shape of a half-moon in front of the southern Bulgarian army. There was no more fighting for the northern army; it was slowly but surely being enclosed, and was now in full retreat along the valley of the river Ibar on the road to Montenegro. Meanwhile the southern army made a last despairing effort to stem the Bulgarian advance in the passes between Prisrend and Monastir, and, having failed, retreated into Albania.