[Sidenote: German methods of making position impregnable.]
During nearly two years' preparation he had spared no pains to render these defenses impregnable. The first and second systems each consisted of several lines of deep trenches, well provided with bomb-proof shelters and with numerous communication trenches connecting them. The front of the trenches in each system was protected by wire entanglements, many of them in two belts forty yards broad, built of iron stakes interlaced with barbed wire, often almost as thick as a man's finger.
The numerous woods and villages in and between these systems of defense had been turned into veritable fortresses. The deep cellars, usually to be found in the villages, and the numerous pits and quarries common to a chalk country were used to provide cover for machine guns and trench mortars. The existing cellars were supplemented by elaborate dugouts, sometimes in two stories, and these were connected up by passages as much as thirty feet below the surface of the ground. The salients in the enemy's lines, from which he could bring enfilade fire across his front, were made into self-contained forts, and often protected by mine fields, while strong redoubts and concrete machine-gun emplacements had been constructed in positions from which he could sweep his own trenches should these be taken. The ground lent itself to good artillery observation on the enemy's part, and he had skillfully arranged for cross-fire by his guns.
[Sidenote: A composite system of great strength.]
These various systems of defense, with the fortified localities and other supporting points between them, were cunningly sited to afford each other mutual assistance and to admit of the utmost possible development of enfilade and flanking fire by machine guns and artillery. They formed, in short, not merely a series of successive lines, but one composite system of enormous depth and strength.
[Sidenote: Many lines prepared in the rear.]
Behind this second system of trenches, in addition to woods, villages, and other strong points prepared for defense, the enemy had several other lines already completed; and we had learned from aeroplane reconnoisance that he was hard at work improving and strengthening these and digging fresh ones between them and still further back.