By late September 1916, the 9th Army was preparing to cross the Carpathians and invade the Old Kingdom of Romania itself. Between them and the plains of central Romania stood however the Romanian 2nd Army, with its 96 battalions, 23 cavalry squadrons and 258 guns ( only 18 were 15 cm pieces, the rest were either 75 or 100 mm weapons ). With the help of the local population, the Romanians dug in and waited for the inevitable German assault. Though the German troops were not numerically superior ( 56 battalions and 8 cavalry squadrons plus some 20 Austro-Hungarian battalions ) they had overwhelming superiority in artillery ( 381 guns including 84 heavy ) but most of all in automatic weapons of all kinds. General von Falkenhayn intended to smash through the center of the front and split Romania in half. If he succeeded, Bucharest and the oilfields near Ploiesti would be within easy reach of the Central Powers.

On the 28th of September, the German forces attacked all over the front, but in most sectors were repulsed with serious losses. Only the 51st Hungarian and 187 German divisions achieved a few kilometers penetration in the western areas, but in the end all enemy forces were stopped and no pass was under German control on the 23rd. After the 12 Bavarian Division arrived to bolster the numbers of the invaders, the 76 German division acting in cooperation with the 8th Austro-Hungarian mountain brigade captured the major town of Brasov ( still inside Transilvania ) plus a few mountain villages, but on the 14th and 15th the Romanian troops counterattacked with such ferocity that the Hungarian unit was forced to pull back from Leresti and eventually was thrown back to its starting positions. The men of the 70th Infantry Regiment, who could literally see their homes from the trenches distinguished themselves during the action.

Following the failure of the overextended Germans to break out of the mountains into the plains, the German commander switched the main axis of attack to the west, attacking from Banat into Oltenia and western Romania. There, he achieved local superiority in men in equipment and launched its new offensive on the 10th of October, after a powerful barrage. For four days, the Germans slowly gained ground as the hard-pressed Romanian 11th Infantry Division pulled back under the weight of the onslaught. The heaviest fighting erupted on the 14th, when the enemy crossed the river Jiu and menaced the city of Tg. Jiu itself. At that moment, the civilian population ( mostly elderly men and teenagers but there are reports that even women took part in the fighting ) rushed forward to aid the regular units. For an entire afternoon, these untrained men, armed with hunting rifles, weapons taken from the dead and generally anything they could get their hands on, held their ground against powerful German assaults until parts of the 59th Infantry Regiment arrived and repulsed the enemy for good. As the overconfident Germans got cocky and failed to realize their flanks were now dangerously exposed to counterattacks, the Romanian commander, general Dragalina, launched a counter strike and by nightfall was about to encircle two German divisions. Panicked, the enemy troops pulled back in disarray, as even Falkenhayn had to admit in his memories "We could barely save the horses. For the guns and vehicles there was nothing we could do : those had to be destroyed or thrown off the steep cliffs..". 2000 German POW's were taken as well as large amounts of weapons and equipment.

The defense of the mountain passes in October 1916 was amongst the finest actions fought by Romanian troops in World War One. The men showed remarkable courage and determination as they fought to defend their homes, the higher echelons ( most of them, unfortunately some incompetents had still not been removed ) demonstrated ingenuity and flexibility both in attack in defense.