Joffre had rewritten Plan XVI by 6 September, increasing the number of troops on the Belgian frontier (although not by as much as Michel had advocated), by shifting forces from the Italian border and incorporating second line and reserve units into the front line. The Fifth Army was to assemble further left to Mézières and the Sixth Army was to move closer to Verdun and the Belgian border west of Luxembourg. The amended version of Plan XVI put seven corps close to Belgium, which guarded against a German advance around Verdun or as far as Verdun or Mézières and Joffre increased emphasis on an immediate offensive. Joffre continued to work on the plan and the possibility of a German move through Belgium, in which three alternatives were inferred, that the Germans would respect Belgian and Luxembourgeois neutrality and attack the Belfort–Épinal and Toul–Verdun lines or advance through Luxembourg in the vicinity of Verdun, then make a smaller attack into Belgium or defend in Lorraine and attack through Belgium. The third possibility was considered likely, because the French knew that a recent German war game had used the German fortifications around Metz and Thionville. German improvements to the fortifications at Metz and Thionville, led Joffre to believe that the Germans certainly would attack through Belgium and also that Belgium was the only place where France could fight a decisive battle against Germany.