The Thionville sector was part of the larger Fortified Region of Metz, a strongly defended area between the Ardennes to the west and the Sarre valley to the east. The Metz region was more important during the planning and construction phase of the Maginot Line than it was in the operational phase of the Line, when the sectors assumed prominence. The Fortified Region of Metz was dissolved as a military organization on 18 March 1940.