Sarrail recognized his danger and began to retire his northern units, covering the movement with a fiercely contested action in the region of Strumitza. [Illustration: A British hydroplane returning to the mother ship after patrol duty over Saloniki. In the background are the City of Saloniki and warships of the Allies.] By December 11, 1915, the French and British lines were close back on the Greek frontier, and although the Bulgarians delivered a heavy attack on that day, it was their final effort; the following day the Allies were across the frontier and the Bulgarians made no attempt to follow them. Possibly they were restrained by their German allies, or possibly they had no desire to involve Greece, for had the Bulgarians set foot on Greek soil, it is more than likely that Greek troops would have resisted them, and once such an encounter had taken place, Greece would probably have thrown herself into the war on the side of the Allies. As they retired, the allied troops destroyed the railroad behind them and set fire to Gevgheli and other towns on the other side of the border. And, by a fortunate coincidence, it was on the day before they crossed the frontier that Greece had finally accepted the proposals of the Allies that their forces were to be allowed freedom of movement. Considering the tremendous difficulties he had had to contend with, in the face of the immense strength of his enemy, General Sarrail's retreat by no means diminished his reputation as a military leader. Although his men had at their disposal only one single-track line of railroad and no roads, their retirement was conducted in such order that they were able to save and withdraw all their stores, while the total of their casualties did not exceed 3,500, a very moderate loss under the circumstances. In less skillful hands the retreat might easily have developed into an irretrievable disaster. In its main object, saving Serbia from being crushed, the campaign had certainly been a failure, but this was rather the fault of the allied governments, and not because of the inefficiency of the leaders in the field. The Bulgarians, naturally, felt that they had attained a great victory, and in a measure they had. On December 14, 1915, they published their version of the operations as follows: