Antwerp fell amid a fluid front. On 9 October Maud'huy's 10th Army was holding up in front of Arras; but his Territorials were falling back on Lille and its environment as the Belgians retreated to join Rawlinson at Ostend. French's three corps were on their way to prolong and establish Maud'huy's left, and an 8th French army under D'Urbal was designed to fling the line yet farther north. But the Germans were bent on a similar object, and their masses of cavalry, released from the front on the Aisne by its settlement into trenches, were keeping open the country and the issue. The rival armies were like two doors swinging towards one another on the same hinge; but they were not wooden or rigid, and the banging together began at the hinge near La Bassée and extended northwards to the coast in a concussion spread over several days. On 11 October Smith-Dorrien's 2nd Corps reached the La Bassée Canal between Aire and Béthune, while Gough's cavalry was clearing the German patrols out of the forest of Nieppe. On the 12th he attempted a frontal attack on La Bassée, but found the German position too strong, and determined to try to wheel round it on the north. This movement had some success; the 3rd Division drove the Germans from village to village until on the 17th Aubers and Herlies, north to north-east of La Bassée, were taken by assault. But the Germans were simultaneously and in the same way driving in the French Territorials; on the 13th they occupied Lille, and on the 19th an Irish brigade which had advanced beyond Herlies to Le Pilly was cut off and captured. So far as the 2nd Corps was concerned the doors had banged together.
Pulteney's 3rd was moving towards collision on the left. It detrained from St. Omer on the 11th, drove the Germans out of Meteren on the 13th, occupied Bailleul and Armentières and then crossed the Lys, gaining a line from Le Gheir, north of Armentières, to Bois Grenier by the 17th. An attempt to clear the right bank farther north failed against the opposition of the German front from Radinghen to Frelinghien and thence along the river. Here, too, the way was barred, but north of the Lys there was as yet no stable control. There were some French and British cavalry and some weak detachments of infantry; but Haig's 1st Corps had not yet completed its transport from the Aisne, Rawlinson's 7th Division was being expanded into a 4th Corps, and the Belgian Army was painfully making its retreat from Antwerp. On the 13th Von Beseler was in Ghent, on the 14th in Bruges, and on the 16th in Ostend. The outflanking here was being done by the Germans with uncomfortable rapidity. On the day that the Germans entered Ostend, the Belgians were driven out of the forest of Houthulst and took refuge far behind the Yser. Four French cavalry divisions recovered the forest on the 17th, but the 7th British Division which had occupied Roulers on the 13th was driven back to a line south-east of Ypres running through Zandvoorde, Gheluvelt, and Zonnebeke (see Map, p. 288).