The Battle of Aisne had stabilized the section of battle-front which ran West from Verdun to Noyon, and beginning with the Battle of Picardy (September 22-26), both the Germans and the Entente forces hoped to extend the West end of their line quickly North in order to gain the upper hand. Picardy had demonstrated, however, that such hopes were likely to be dampened by the blood of both armies.
Following Picardy, the active battle-front shifted just to the North as the opponents sought an unprotected flank. The resultant Battle of Albert (September 25-29) was so fast and so fierce that neither of the opponents had time to count their losses . . . troops attacked almost as quickly as they could arrive to the area, and when the contest had finally ended in an obvious draw, the opponents quickly dug trenches in whatever ground they occupied, regardless of defensibility (or the lack thereof).
Another result of the hasty extension of the lines Northward was the (sometimes temporary) appointment of new commanders to the troops quickly sent to the active flank attacks. The West flank during the Battle of Aisne, for example, had been commanded by Alexander von Kluck for the Germans, and Michel-Joseph Maunoury for the French. During the race Northward, on the other hand, both the French and the Germans had to snatch whatever commander was least pre-occupied and rush him to the active area to command the troops sent there to extend the lines.
For this Germans, this was the Crown Prince of Bavaria, Rupprecht (Rupert) Maria Luitpold Ferdinand.
And his French counterpart there was Noël Edouard Marie Joseph de Castelnau (often simply called Edouard Castelnau.
At this point, the Western front looked a bit like this: