On the 13th, amidst drenching rain, and in teeth of a bitter north wind, they returned to the assault. They had broken the German line; but their work was by no means done, for though the trenches had been carried, the German forts all along the front still held out, and each of them had to be besieged. The strongest position of all lay to the south of Neuville, and was known as the Labyrinth.[39] It was a wonderful network of trenches and redoubts, tunnels and roofed-in pits; it covered two square miles, and was so situated that the long-range fire of the French artillery could not get at it. Probably never before had such a stronghold been constructed. It was a cunning maze, furnished with every death-dealing device known to the science of war. It contained engines for making poison gas, machines for throwing liquid fire, scores of small fortresses, and underground passages which enabled the defenders to get to the rear of the attackers. In the background an enormous collection of big guns was in position, ready to sweep away any troops advancing upon it. Such was the Labyrinth which the French were attacking. They could not proceed until it was captured, for, as you will observe from the map on page 223, it enfiladed their advance. By the end of May good progress had been made in clearing the Labyrinth. The German salient had gone, the French line had been straightened out, and Lens was closely beset. An officer gives us a vivid picture of the struggle in the Labyrinth, which was not captured till towards the end of September:-- "The war of trenches is nothing compared with the struggle of the burrows. Picture to yourselves narrow galleries, feebly lighted by flickering oil lamps, in which the foes are separated only by sand-bags, which they keep pushing against each other. As soon as an opening shows, a terrific hand-to-hand fight begins, in which grenades and the bayonet are the only arms possible. Sometimes the Germans take to knives and revolvers, and one day they even began throwing burning liquids; but in spite of these cowardly tricks, our men always had the best of it. They fought with clubbed rifles and fists when required, and their courage was never shaken, as the Germans soon saw. . . .