The position which the British had captured was exceptionally strong, consisting of a double line, including some large redoubts and a network of trenches and bomb-proof shelters. Dugouts were constructed at short intervals all along the line, some of them being large caves thirty feet below the ground. The French capture of Souchez was an event of considerable importance, for the German High Command had issued orders for this section to hold on to the last, that it was to be retained at all costs. The road to the Douai plain was to be barred to the French, who had to be held back behind the advanced works of the Artois plateau. In May, 1915, the problem was to prevent the French setting foot on the summits of Notre Dame de Lorette and of the Topart Mill. The Germans sacrificed many thousands of men with this object, but the French nevertheless made themselves masters of the heights which the Germans considered of capital importance, and dislodged them from Carency and Ablain-St. Nazaire. There remained only one stage to cover--the Souchez Valley--to reach the last crest which dominated the whole country to the east, and beyond which the ground is flat. This task had been accomplished during the last few days of September and the beginning of October. Souchez and its advanced bastion, the Chateau Carleul, had been made into a formidable fortification by the changing of the course of the Carency streams. The Germans had transformed the marshy ground to the southeast of this front into a perfect swamp, which was regarded as impassable. The German batteries posted at Angres were able to enfilade the valley on the north. From behind the crest of Hill 119 to Hill 140, which were covered with trenches connected by a network of communication trenches, many batteries were engaged against the French in the district of Notre Dame de Lorette, Ablain-St. Nazaire and Carency. To the north of Souchez the German trenches were still clinging to the Notre Dame de Lorette slope.