Joffre set 14 August as the date when the First and Second armies were to invade Lorraine between Toul and Épinal, south of the German fortified area of Metz-Thionville. The First Army was to attack in the south with four corps, towards Sarrebourg east of Nancy and Donon south of Sarrebourg. Passes in the Vosges to the south of Donon were to be captured before the main advance began. The Second Army was to attack towards Morhange north-east of Nancy, with two corps north of the First Army and three advancing successively behind the left flank of the corps to the south, to counter a German attack from Metz. The French offensive was complicated by the two armies diverging as they advanced, on difficult terrain particularly in the south, the combined fronts eventually being wide. The advances of the First and Second armies were to attract German forces towards the south, while a French manoeuvre took place in Belgium and Luxembourg, to pierce a weak point in the German deployment and then destroy the main German armies.