The First Battle of the Marne was a battle of the First World War fought from 6 to 12 September 1914. It resulted in an Allied victory against the German armies in the west. The battle was the culmination of the Retreat from Mons and pursuit of the Franco–British armies which followed the Battle of the Frontiers in August and reached the eastern outskirts of Paris.
Field Marshal Sir John French, commander of the British Expeditionary Force, began to plan for a full British retreat to port cities on the English Channel for an immediate evacuation. The military governor of Paris, Joseph Simon Gallieni, wanted the Franco–British units to counter-attack the Germans along the Marne River and halt the German advance. Allied reserves would restore the ranks and attack the German flanks. On 5 September, the counter-offensive by six French armies and the British Expeditionary Force began.
By 9 September, the success of the Franco–British counteroffensive left the German 1st and 2nd Armies at risk of encirclement, and they were ordered to retreat to the Aisne River.