Such were some of the difficulties with which I was beset in the rear of my battle line. They were negligible compared with those which now loomed in front of it.
The reach of the Somme which runs northerly from Ham past Brie to Péronne and there turns westerly, differs entirely in its topographical features from that picturesque Somme Valley along both of whose banks the Corps had been fighting its way forward. The steep banks have disappeared, and for a mile or so on either side the ground slopes gently towards the river bed.
The river itself is not less than 1,000 yards wide, being, in fact, a broad marsh, studded with islets which are overgrown with rushes, while the stream of the river threads its way in numerous channels between them. The marsh itself is no more than waist-deep, but the flowing water is too deep to be waded.
Along the western side of this marsh runs the canalized river, or, as it is here known, the Somme Canal, flowing between masonry-lined banks. The construction of a crossing of such a marsh was, even in peace time, a troublesome business. It meant, to begin with, a causeway solidly founded upon a firm masonry bed sunk deep into the mud of the valley bed. The canal itself and each rivulet required its separate bridge, in spans varying from thirty to sixty feet.
What, therefore, came to be known as the Brie Bridge, situated on the line of the main road from Amiens to St. Quentin, really consisted of no less than eight separate bridges disposed at irregular intervals along the line of the causeway, between the western and eastern banks of the valley. The demolition of even the smallest of these eight bridges would render the whole causeway unusable, and would prohibit all traffic.
There exists an almost exactly similar arrangement of bridges at St. Christ, about two miles to the south of Brie, but no other traffic crossing to the north of Brie until Péronne is reached. There, both the main road and the railway, which cross side by side, are provided with large span lattice girder bridges, over the main canal, while the marsh has been reclaimed where the town has encroached upon it. The river overflow is led through the town in several smaller canals or drains, all of them liberally bridged where crossed by roads and streets.
The Péronne bridges are, therefore, no less indispensable, and no less easily rendered useless than those at Brie. Should such crossings be denied to me, it would be just possible to pass infantry across the valley, by night, by wading and swimming, or by the use of rafts, always provided that no opposition were to be met with. But to pass tanks or heavy guns, or even vehicles of the lightest description across the marsh, would have been quite impossible.
The Somme threatened, therefore, to be a most formidable obstacle to my further advance. It was incumbent upon me to assume that at the very least one of each series of bridges would be demolished by the enemy in his retreat. It would have been criminal folly on his part were it to have been otherwise; and I had had previous evidence of the efficiency of his engineer services.
Reconnaissances pushed out on the night of August 29th speedily verified the assumption that some at least of the bridges had been wrecked. It was ultimately ascertained that every single bridge in every one of the crossings named had been methodically and systematically blown to pieces.