These armies had all crossed the Meuse south of the fortress of Namur, and, to retain connexion with them, von Bülow had had to detach a force on his left to seize the line of the Meuse from Liége to Namur and to capture Namur itself. The best German heavy artillery was assigned to this force for the purpose, and _Namur_ fell, after an unexpectedly short bombardment, on Aug. 23rd, while von Bülow’s main army at Charleroi was still engaged in its struggle with the French. The fall of Namur opened the way for German armies to cross the Meuse along the whole line from Namur to Verdun. The first crossing was made at _Dinant_ on Aug. 23rd, the very day on which Namur fell, by a Saxon army, which marched thither by cross routes through Luxembourg; the second by the Duke of Würtemberg’s army between _Mezières_ and _Sedan_; and the third by the Crown Prince of Prussia’s army immediately north of _Verdun_. West of the Meuse the Saxons and Würtembergers amalgamated, and got into touch with von Bülow on their right. Advancing parallel with him, they reached _Charleville_ on Aug. 25th, crossed the Aisne at _Rethel_ on the 30th and the Marne at _Châlons_ on the 4th, and were stopped on the 7th at _Vitry en Perthois_. The Crown Prince, on their left, did not penetrate so far. Instead of the plains of Champagne he had to traverse the hill country of the _Argonne_. He turned back at _Sermaize_, which he had reached on Sept. 6th, and never saw the Marne. On the left of the Crown Prince a Bavarian army crossed the frontier between Metz and the Vosges. Its task was to join hands with the Crown Prince round the southern flank of Verdun, as the Duke of Würtemberg had joined hands with von Bülow round the flank of Namur. But Verdun never fell, and the Bavarian advance was the weakest of any. _Lunéville_ fell on Aug. 22nd, and _Baccarat_ was entered on the 24th; but _Nancy_ was never reached, and on Sept. 12th the general German retreat extended to this south-easternmost sector, and the Bavarians fell back. Thus the German invading armies were everywhere checked and driven back between the 6th and the 12th September, 1914. The operations which came to this issue bear the general name of the _Battle of the Marne_. The _Marne_ was followed immediately by the _Aisne_, and the issue of the Aisne was a change from open to trench warfare along a line extending from the Vosges to the Oise. This change was complete before September closed, and the line formed then has remained practically unaltered to the present time. But there was another month of open fighting between the Oise and the sea.