While Foch had been carrying out his role as commander of XX Corps within Second Army by holding down as many German forces as possible on the eastern frontier, the main battles of August 1914, known collectively as the Battles of the Frontiers, had taken place. By using First and Second Armies in Alsace and Lorraine, Joffre had retained the flexibility to deploy France’s Third and Fourth Armies in the centre and Fifth Army on the left of the line. Joffre knew that German troops were marching through Luxembourg and Belgium, but he did not know their strength or their exact route. As it became clear that the German right wing was stronger than had first been estimated, Joffre drew the conclusion that therefore the centre must have been weakened. First and Second Armies had fulfilled their roles of holding enemy forces admirably, and so, if the German right was indeed stronger, then the forces deployed in front of Third and Fourth Armies in the centre must be weaker. As a consequence, Joffre sent these two armies into Belgium on 21 August (the day after Rupprecht’s attack at Morhange) with orders to attack the enemy wherever he was found. Although Fourth Army was six-corps strong, the opposing German forces were stronger still. Joffre had miscalculated disastrously and the costly Battles of the Frontiers were the result.