The Battle of the Frontiers comprised battles fought along the eastern frontier of France and in southern Belgium, shortly after the outbreak of the First World War. The battles resolved the military strategies of the French Chief of Staff General Joseph Joffre with Plan XVII and an offensive adaptation of the German Aufmarsch II deployment plan by Helmuth von Moltke the Younger. The German concentration on the right (northern) flank, was to wheel through Belgium and attack the French in the rear.

The Battle of the Trouée de Charmes or Battle of the Mortagne was fought at the beginning of the First World War, between 24 and 26 August 1914 by the French Second Army and the German 6th Army, after the big German victory at the Battle of the Frontiers, earlier in August.