Hugh M. Cole, The Ardennes: Battle of the Bulge… (1965)
“ Their valleys are long and narrow, so narrow and tortuous that they cannot be followed by roads. They are further complicated by "cups" scoured out of the side walls and by cross ravines, deep and narrow. In the Ardennes north of Luxembourg it is possible to cross from Germany into Belgium without traversing a major stream. About twenty miles west of the frontier, however, comes the first of the rivers descending from the High Ardennes into the Meuse ”
