15th - 18th September 1914 - The First Battle of the Aisne.

The Allies began to cross the Aisne under heavy fire. They mainly used pontoon bridges, as only one of the permanent crossings remained intact; a bridgehead was established on the north of the river and was soon enlarged. On the following day, 14 September, they made further small gains in an assault on the enemy line, which was located on the plateau above them. However, within hours German counterattacks, with strong artillery support, had pushed back the French Sixth Army almost to its starting position. The Allies were unable to make any real progress against the Germans' well-prepared positions and, with the French also coming under pressure at Reims, this largely stationary battle was abandoned on 18 September.

It was already becoming clear that a frontal assault by infantry alone, without heavy artillery support, was unlikely to be successful. As the Aisne offensive drew to a close Joffre moved his forces north-west in an attempt to attack the exposed German right flank at Noyon; the enemy responded by moving reserves to the area with the aim of outflanking the Allies themselves. Both manoeuvres were unsuccessful but the opposing armies made several further attempts to outflank each other during the so-called 'Race to the Sea', which continued until the Allies reached Nieuport early in October. The Battle of the Aisne and its sequel marked the closing stages of the war of movement and the beginnings of trench warfare.