Bapaume had fallen on March 17th, Péronne on the following day. South and east of Péronne, on the 21st, the Fourth Army had captured forty villages. French troops reached the outskirts of St. Quentin, and counted their villages by the score. The Cavalry, mounted and dismounted, had come in for a bit of their own, and a fine exhilaration of open fighting had been blown like a freshening breeze along the east wall of the shell-torn quadrangle. But after the third week of March the pace of the retreat began to slacken; and, as soon as the first days of April dispelled the cover of the mist, and the wind and the sun dried up the mud from which the Germans had been retiring, their slower pace stiffened into resistance, and their resistance hardened into battle. All along the Hindenburg Line, so much advertised, yet in places so elastic, which was to guard the ridges of observation, the Battle of Arras was engaged in April, May and a part of June, and during the course of that Battle, Bullecourt was won and lost and won again. No more need be said about the retreat. The precise ratio between initiative and compulsion, precisely how far, that is to say, it was carried through according to plan and directed by forces under German control, will not be settled till the official war-histories of both belligerents have been published, and may even be disputed thereafter. Certainly, it was admirably executed; less certainly, it was voluntary in all its parts; most certainly, it was accompanied by incidents which indelibly stained the reputation of the German Military Command. That ‘the systematic destruction of roads, railways and bridges in the evacuated area made unprecedented demands upon the Royal Engineers,’ or that in four and a half days, for example, from the morning of March 18th the Somme at Brie was rebridged for our troops,[73] were facts of warfare as legitimate for the enemy as they were creditable to his pursuers. What was illegitimate and irreparable was the not less systematic destruction, forbidden in the Pentateuch, as Mr. Buchan[74] notes, of ‘trees for meat’ and water for drinking. We have remarked these features _in petto_: the single trees felled or slashed, the single wells poisoned or blown in, the single monuments gutted or mined; and France knows the full tale of her own wrongs. So we come to the Battle of Arras, which opened definitely on April 9th and rolled in thunder along the northern ridges to its renewed flood in the Third Battle of Ypres.