Tourcoing by Hilaire Belloc

The terrain over which the plan of the allies was to be tested must next be grasped if we are to understand the causes which led to its ultimate failure.

That terrain is most conveniently described as an oblong standing up lengthways north and south, and corresponding to the sketch map overleaf. That oblong has a base of twenty miles from east to west, a length from north to south of thirty-five.