the Fourth Reserve Group guarding the northern flank near Hirson, to watch the Chimay Gap and deflect a German attack from the north or east. The strategy assumed that the main German force would be deployed around Luxembourg and from Metz–Thionville, with smaller forces in Belgium. On 9 August, an intelligence report had one German active corps near Freiburg close to the Swiss border, three near Strasbourg, four in Luxembourg to the north of Thionville and six from Liège in Belgium, towards the north end of Luxembourg, which left five corps un-located. The French general staff inferred that they were between Metz-Thionville and Luxembourg, ready to advance towards Sedan or Mézières. 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. News that German forces were attacking towards the Meuse bridges south of Namur, led Joffre to expect a German attack from Mézières to Givet, further north, intended to envelop the French northern flank and another force to try to cross the Meuse from Montmédy to Sedan. On 12 August, Joffre allowed Lanrezac to move the I Corps west to Dinant on the Meuse and on 15 August, Joffre ordered the bulk of the Fifth Army to move north-west behind the Sambre. No large German force was expected to cross to the north of the Meuse, which made the French general staff certain that the German centre was weaker than expected. On 18