day (23 September), the German Alpine Corps began their march through the mountains to the Red Tower pass, behind Romanian lines. During the march of the German Alpine Corps, the left of the Central Powers forces - the German column which was to encircle the Romanians from the east - succeeded in forcing the crossing of the Olt River at Kolun (Colun/Kellen), east of Porumbák. Thus, an effective barrier was created between the 1st and the 2nd Romanian armies. In its advance across the mountain ridge separating the valleys of the Hortobágy (Hârtibaciu/Haarbach) and Olt Rivers, this German column was faced with determined resistance. Still, its numerical superiority enabled it to prevail. By the evening of 25 September, Kolun was in German hands. Falkenhayn's plan On 19 September, Erich von Falkenhayn assumed command of the German 9th Army. This army subsequently started assembling the bulk of its forces near Nagyszeben. Von Falkenhayn divided his forces into three groups: the XXXIX Reserve Corps, the Alpine Corps and Cavalry Corps Schmettow. His plan was bold: the annihilation of the Romanian units around Nagyszeben. Konrad Krafft von Dellmensingen's Alpine Corps Division was to act as an anvil, seizing the Red Tower Pass in order to block a Romanian retreat. Hermann von Staabs's Corps, assembling northwest of Nagyszeben, was to act as a hammer, driving southeast towards the mouth of the Red Tower Pass at Nagytalmács (Tălmaciu/Talmesch). With the Alpine Corps blocking the Romanian line of retreat, the XXXIX Corps would smash the Romanians against the mountains. Von Schmettow's cavalry had to maintain contact with the Austro-Hungarian 1st Army, make sure that none of the Romanians escaped east, and block any reinforcements coming from the Romanian 2nd Army, threatening the 9th Army's flank. Popovici relied on the mountains to protect his flanks. However, reconnaissance by the German Alpine Corps revealed that it was possible to bypass his western flank, on foot, through the mountains, then reach and cut off the Romanian line of retreat. This made Popovici's corps the most tempting target, and von Falkenhayn stressed as much: all else was secondary to striking a decisive blow at Nagyszeben. Units involved (forces and deployments) On the Romanian side, General Popovici had two divisions at Nagyszeben: the 23rd Division to the south and west of the highway running from Nagyszeben to the Red Tower Pass and the 13th Division to the east of this highway.