At the outset the Allies dug very shallow ditches, such as had been used in previous wars. When it was found that these burrows would have to be occupied for weeks and months, the French and British imitated the Germans and dug their trenches so deep that men could walk through them freely, without danger of exposing their heads above ground; and as the ditches grew deeper, they had to be provided with a firing-step on which the riflemen could stand to fire over the top of the trenches. The trenches were zig-zagged so that they could not be flanked, otherwise they would have made dangerous traps for the defenders; for had the enemy gained one end of the trench, he could have fired down the full length of it, killing or wounding every man it contained. But zig-zagging made it necessary to capture each turn separately. There were lines upon lines of these trenches. Ordinarily there were but three lines, several hundred feet apart, with communicating trenches connecting them, and then several kilometers[1] farther back were reserve trenches, also connected by communicating trenches with the front lines. [1] A kilometer is, roughly, six tenths of a mile; or six miles would equal ten kilometers. Men did not dare to show themselves out in the open near the battle-front for a mile or more behind the front-line trenches, for the enemy's sharp-shooters were always on the watch for a target. The men had to stay in the trenches day and night for two or more weeks at a time, and sleeping-accommodations of a very rough sort were provided for them in dugouts which opened into the trenches. The dugouts of the Allies were comparatively crude affairs, but the Germans spent a great deal of time upon their burrows. UNDERGROUND VILLAGES When the French first swept the Germans back out of their trenches along the Aisne, they were astonished to find how elaborate were these underground dwellings. They found that the ground was literally honeycombed with rooms and passageways. Often the dugouts were two stories in depth and extended as much as sixty feet below the level of the ground. In fact, all along this part of the front, the Germans had a continuous underground village in which thousands of men were maintained. The officers' quarters were particularly well fitted up, and every attention was given to the comfort of their occupants. There were steel door-mats at the entrances of the quarters. The walls were boarded and even papered. The bedrooms were fitted with spring beds, chiffoniers, and wash-stands, and all the rooms were lighted with electric lamps. There were spacious quarters for the men, with regular underground mess halls and elaborate kitchens. There were power-plants to furnish steam for the operation of pumps and for the lighting-plants and for other purposes. [Illustration: (C) Underwood & Underwood Lines of Zig-Zag Trenches as viewed from an Airplane]