At the end of August 1914, the three armies of the German invasion's northern wing were sweeping south towards Paris. The French 5th and 6th Armies and the British Expeditionary Force (BEF) were in retreat. General Alexander von Kluck, commander of the German Ist Army, was ordered to encircle Paris from the east. Expecting the German army to capture Paris, the French government departed for Bordeaux. About 500,000 French civilians also left Paris by the 3rd September.
Joseph Joffre, the Commander-in-Chief of the French forces, ordered his men to retreat to a line along the River Seine, south-east of Paris and over 60km south of the Marne. Joffre planned to attack the German Ist Army on 6th September and decided to replace General Charles Lanrezac, the commander of the 5th Army, with the more aggressive, General Franchet D'Esperey. The commander of the BEF,Sir John French, agreed to join the attack on the German forces.
General Michel Maunoury and the French 6th Army attacked the German Ist Army on the morning of 6th September. General von Kluck wheeled his entire force to meet the attack, opening a 50km gap between his own forces and the German 2nd Army led by General Karl von Bulow. The British forces and the French 5th now advanced into the gap that had been created splitting the two German armies.
For the next three days the German forces were unable to break through the Allied lines. At one stage the French 6th Army came close to defeat and were only saved by the use of Paris taxis to rush 6,000 reserve troops to the front line. On 9th September General Helmuth von Moltke, the German Commander in Chief, ordered General Karl von Bulow and General Alexander von Kluck to retreat. The British and French forces were now able to cross the Marne. Despite encountering little opposition, the advance was slow and the armies covered less than twelve miles on that first day. This enabled Kluck's Ist Army to reunite with Bulow's forces at the River Aisne.
By the evening of 10th September, the Battle of the Marne was over. During the battle, the French had around 250,000 casualties. Although the Germans never published the figures, it is believed that Geman losses were similar to those of France. The British Expeditionary Force lost 12,733 men during the battle.
The most important consequence of the Battle of the Marne was that the French and British forces were able to prevent the German plan for a swift and decisive victory. However, the German Army was not beaten and its successful retreat ended all hope of a short war.