and ringed with masses of heavy artillery, inevitably leading to huge losses and bringing the French army close to collapse. The British would have no choice but to begin a hasty relief offensive, to divert German attention from Verdun but would also suffer huge losses. If these defeats were not enough, Germany would attack both armies and end the western alliance for good. The unexpected length and cost of the Verdun offensive and the underestimation of the need to replace exhausted units there, depleted the German strategic reserve placed behind the 6th Army, which held the front between Hannescamps south-west of Arras and St Eloi, south of Ypres and reduced the German counter-offensive strategy north of the Somme to one of passive and unyielding defence. On the Eastern Front the Brusilov Offensive began on 4 June and on 7 June a German corps was sent to Russia from the western reserve, followed quickly by two more divisions. After the failure to capture Fort Souville at Verdun on 12 July, Falkenhayn was obliged to suspend the offensive and reinforce the defences of the Somme front, even though the 5th Army was on the brink of the strategic objectives of the offensive. The British–French plan for an offensive on the Somme front had been decided at the Chantilly Conference of December 1915 as part of a general Allied offensive by the British, French, Italians and Russians. British–French intentions were quickly undermined by the German offensive at Verdun which began on 21 February 1916. The original proposal was for the British to conduct preparatory offensives in 1916 before a great British–French offensive from Lassigny to Gommecourt, in which the British would participate with all the forces they still had available. The French would attack with on a front of and the British with on on the northern French flank. The course of the battle at Verdun led the French gradually to reduce the number of divisions for operations on the Somme, until it became a supporting attack for the British on a front with only five divisions. The original intention had been for a rapid eastwards advance to the higher ground beyond the Somme and Tortille rivers, during which the British would occupy the ground beyond the upper Ancre. The combined armies would then attack south-east and north-east, to roll up the German defences on the flanks of the breakthrough. By 1 July,