It was at this moment that the defeat of the enemy began to take shape. A great part of the Vardar-Cerna triangle was lost, the few troops remaining between Demir Kapu and Ghevgheli had now to fall back beyond the Vardar in a north-easterly direction, and this fact constituted a menace even for the troops round Lake Doiran, to whom no other line of supply was left but the Doiran-Kosturino-Strumitza road. On the 21st signs that a retreat was beginning were noted on the British front. Everywhere depots were observed to be in flames, and munitions dumps exploding. General Milne, with his XII Corps strengthened by the 14th Greek Division, renewed the offensive. The 9th Bulgarian Division having offered but slight resistance, the formidable defences collapsed without much effort, and the whole II Bulgarian Army fell back, seeking safety over the narrow Kosturino Pass. While the British infantry and cavalry pursued them, flights of aeroplanes, flying only a few metres from the ground, bombarded the Bulgarians and shot down men with machine guns along the Strumitza road, encumbered with vehicles, artillery, etc., by now in indescribable disorder. The spectacle offered by that road was one of appalling confusion and terror. From all sides fires broke out; guns were abandoned in gullies, rifles, equipment, baggage were thrown away, and the demoralized army fled towards its homeland. On the 21st the A.F.O. came into action. The enemy troops on this sector were less threatened than on the other sectors, because, if they had lost the Prilep-Gradsko road, they still retained that over the Babuna Pass between Prilep and Veles, which could be easily defended, and the Kichevo-Kalkandelen road. But they were now threatened in another quarter. Day by day the communications between the XI German Army and Bulgaria were becoming more difficult, and it could be foreseen that at any moment they might be cut altogether, and then that Army would have had no other alternative but to retreat across Albania to reach the Herzegovina and Dalmatia. It was the fate of the Serbian Army in 1915 which seemed about to be repeated. On that day detachments of the 11th Colonial Division (General Farret) and the 3rd Greek Division (General Tricoupis) crossed the Cerna (east) between Selo-Monastir and Cebren, and advanced in the direction of Prilep. General Henrys, commanding the A.F.O., now ordered the advance of his whole army, beginning with an attack launched by the Italian Expeditionary Force.