The deadlock was no part of the original German plan, but German forethought during the advance to the Marne had provided entrenchments in the rear for the event of a retreat, and the natural strength of the forest of St. Gobain, the Chemin des Dames, and the Argonne as well as a study of the campaign of 1814 had suggested an obvious line of defence. It was not, however, expected by the Entente higher command which proceeded with its frontal attack on the assumption that the Germans were merely fighting rearguard actions to secure their further retirement; and it was only when the German front refused to budge that pressure spread out to the Allied left wing in an attempt to turn the German right flank, which would have stood more chance of success had it come a fortnight earlier as a first instead of a second thought. An even better alternative might have been to revert to Joffre's original plan, which had failed in August on the Saar, to thrust forward against the Crown Prince and threaten the left of the Germans and the communications of their forces in Belgium and northern France. But it is easier on paper after the event than it was in action at the time to convert an improvised defensive into a considered offensive strategy; and the Germans themselves had occasion during the autumn and the rest of the war to regret that their second thoughts had not come first. The battle of the Aisne began, like that of the Marne, on Sunday, 13 September. The Germans' retreat had taken them north of the river except at a few bridgeheads, but the river was deep and its crossings were all commanded by fire from German batteries concealed on the slopes rising up from the northern bank. Maunoury's 6th Army attacked on the left from Compiègne and the Forêt de l'Aigle to Soissons, and several divisions were got across. From Soissons eastward for fifteen miles to Pont-Arcy the line of attack was held by the British Army; the whole of the 4th Division got across near Venizel, and most of the 5th and 3rd Divisions farther east, but the Germans succeeded in holding the bridge at Condé. The 2nd Division was also only partially successful in the region of Chavonne, but the whole of the 1st got across at Pont-Arcy and Bourg. On Monday, Maunoury pressed forward up the heights, capturing Autrèches and Nouvron, but, like the British on his right between Vregny and Vailly, he found the German positions impregnable on the plateau. Haig's First Corps was more successful farther east; Vendresse and Troyon were captured and the Chemin des Dames was almost reached. But D'Esperey's 5th French army could make little impression on the Craonne plateau; Foch's 9th was unable to force the Suippe to the east of Reims, and Langle's 4th, while it occupied Souain, was similarly held up in Champagne.