We have said that in the original battle scheme, certain points of vantage, Quennemont, the Knoll, and Bellicourt, were assumed to be in our hands a day or so before the main attack on the 4th Army front was launched. These fortified heights were of importance owing to the singular geography of this sector of the line. All along this piece of the front, more or less parallel to the lines of the armies, runs--deep and broad--the St. Quentin Canal. For three and a half miles, however, between Bellicourt and Vendhuille it runs underground through a tunnel. We have seen how, in the northern part of the line, the enemy had relied upon the Canal du Nord to form the principal obstacle to an attack. In August we had captured a document which proved that he realised that if we attacked at all in the south, and whether we attacked with Tanks or not, it would be in that three-and-a-half-mile gap that our heaviest blow would fall. The photograph gives an excellent notion why we had to avoid certain sectors of the Canal at all costs, and Sir Douglas Haig, in his Despatch, gives an admirable idea of some of the complex features which the topography here possessed. “The general configuration of the ground through which this sector of the Canal runs, produces deep cuttings of a depth in places of some sixty feet; while between Bellicourt and the neighbourhood of Vendhuille the Canal passes through a tunnel for a distance of 6000 yards. In the sides of the cuttings the enemy had constructed numerous tunnelled dug-outs and concrete shelters. Along the top edge of them he had concealed well-sited concrete or armoured machine-gun emplacements. The tunnel itself was used to provide living accommodation for troops, and was connected by shafts with the trenches above. South of Bellicourt the Canal cutting gradually becomes shallow, till at Bellenglise the Canal lies almost at ground level. South of Bellenglise the Canal is dry. “On the western side of the Canal, south of Bellicourt, two thoroughly organised and extremely heavily wired lines of continuous trench run roughly parallel to the Canal, at average distances from it of 2000 and 1000 yards respectively. The whole series of defences, with the numerous defended villages contained in it, formed a belt of country varying from 7000 to 10,000 yards in depth, organised by the employment of every available means into a most powerful system, well meriting the great reputation attached to it.” On the three and a half miles of front, where alone Tanks and artillery could cross the line of the Canal, the outpost system which everywhere protected the Hindenburg Line, was doubly reinforced, and gained a natural strength from its position on the heights, beneath which the Canal had burrowed.