South of the Somme, the situation was still more critical. The remains of the British 18th and 19th Corps withdrew to the line Chaulnes-Frise, which they were, however, unable to hold. Their retreat continued to the line Proyart-Rosières. No more reserves were expected for four days. Should the Germans succeed in crushing these exhausted units the road to Amiens would be open. About six miles behind the Proyart-Rosières front, there was an old French line, partly filled in, on the Santerre Plateau, between the Somme (at Sailly-le-Sec) and the Luce (at Demuin). A battalion of Canadian Engineers was ordered to restore it. However, there were no troops to hold it, and as its abandonment would have imperilled Amiens, Gen. Gough decided to muster an emergency detachment of engineers, miners, electricians, mechanics, staff personnel, pupils and instructors from the schools of the 3rd and 5th Armies, and American sappers, in all about 2,200 men. This detachment, under Maj.-Gen. Carey, was ordered to hold an eight-mile front and bar the road to Amiens. North of the Somme, the Germans attacked from Ervillers to the river; the British left stood firm, whilst on the right, the hinge formed by Byng's Army, likewise resisted. Further south, the Germans captured Maricourt, and broke through the curtain of British troops, which lost contact with one another. The Ancre was crossed, and Byng's right, pivoting on Boyelles, fell back on the line Bucquoy, Albert, Bray-sur-Somme. General Pétain issued a stirring appeal to the men: _The enemy is attacking in a supreme effort to separate us from the British, and open the road to Paris. At all cost, he must be held. Stick to the ground, stand firm, reinforcements are at hand. United, you will fling yourselves on the invader. Soldiers of the Marne, Yser and Verdun, the fate of France is in your hands._ From all parts of the front, French divisions poured in. Long lines of motor-lorries sped along all the roads converging towards Montdidier. The high spirits and fine bearing of the men reassured the anxious population, who, for several days past, had heard the guns drawing nearer, and seen the endless stream of refugees fleeing before the invader. General Debeney arrived with his staff from Toul, to take command of the 1st Army (in formation), divisions of which arrived each day. [Illustration] The 77th. Inf. Div. (d'Ambly) was added to the 3rd Army (Humbert). The operations of these two armies, whose task it was to bar the road to Paris and cover Amiens, were co-ordinated by Gen. Fayolle. The Push towards Montdidier and Fall of Roye. The Push towards Amiens and Fall of Albert. On the =26th=, Gen. Pellé's group occupied Mont Renaud--a natural rampart protecting the valley of the Oise. Determined to force a passage at all cost, the enemy attacked with fresh troops.