Complex sentence: The following day, the French 1st Army arrived near Gembloux, near Hannut, to cover the "Gembloux gap", a flat area of terrain, devoid of prepared or entrenched positions.
Split into simpler sentences: The following day, the French 1st Army arrived at Gembloux, near Hannut, to cover the "Gembloux gap". It was a flat area, devoid of prepared or entrenched positions.