The eastern hills of France, those pleasant rolling heights above Rheims, Verdun, and old, provincial Pont-a-Mousson, have been literally gorged with blood.  It being out of the question to strengthen or rectify very much the front-line trenches close to the enemy, the effort has taken place in the rear lines.  Wherever there is a certain security, the rear lines of all the important strategic points have been converted into veritable subterranean fortresses.  The floor plan of these trenches is an adaptation of the military theory of fortification—­with its angles, salients, and bastions—­to the topography of the region.  The gigantic concrete walls of the bomb-proof shelters, the little forts to shelter the machine guns, and the concrete passages in the rear-line trenches will appear as heavy and massive to future generations as Roman masonry appears to us.  There are, of course, many unimportant little links of the trench system, upon whose holding nothing depends and for whose domination neither side cares to spend the life of a single soldier, that have only an apology for a second position.  The war needs the money for the preparation of important places.  At vital points there may be the tremendously powerful second line, a third line, and even a fourth line.  The region between Verdun and the lines, for instance, is the most fearful snarl of barbed wire, pits, and buried explosives that could be imagined.  The distance would have to be contested inch by inch.

The trench theory is built about the soldier.  It must preserve him as far as possible from artillery and from an infantry attack.  The defenses begin with barbed wire; then come the rifles and the machine guns; and behind them the light artillery, the “seventy-fives,” and the heavy artillery, the “one hundred and twenties,” “two hundred and twenties,” and, now, an immense howitzer whose real caliber has been carefully concealed.  To take a trench position means the crossing of the entanglements of No Man’s Land under fire from artillery, rifles, and machine guns, an almost impossible proceeding.  An advance is possible only after the opposing trenches have been made untenable by the concentration of artillery fire.  The great offensives begin by blowing the first lines absolutely to pieces; this accomplished, the attacking infantry advances to the vacated trenches under the rifle fire of those few whom the terrible deluge of shells has not killed or crazed, works toward the strong second position under a concentrated artillery fire of the retreating enemy as terrible as its own, fights its way heroically into the second position, and stops there.  The great line has been bent, has been dented, but never broken.  An offensive must cover at least twenty miles of front, for if the break is too narrow the attacking troops will be massacred by the enemy artillery at both ends of the broken first lines.  If the front lines are one mile deep, the artillery must put twenty-five