north of Lake Ostrovo. General Maurice Sarrail now prepared a counterattack against the First Bulgarian Army that would eventually develop in the Monastir Offensive. The blow was to be directed against the right wing of the First Army which consisted of the Third infantry brigade of the 6th "Bdin" division, the Third cavalry brigade and the 8th "Tundzha" and First infantry brigade of the Third "Balkan" infantry division or in total about 36 infantry battalions, 74 machine guns and 35 artillery batteries. Against them were arrayed the Serbian Third Army and the divisional group of general Cordonnier. The offensive began with the battle of Malka Nidzhe on 12 September 1916. After two days of fighting the Serbians achieved a breakthrough around Gornichevo and forced the Bulgarian 8th division to retreat. Meanwhile, the battle for Kajmakcalan also began. The fall of Florina on 23 September and the retreat of the Bulgarian First Army forced some changes in the Central Powers command structure. On 27 September general Kliment Boyadzhiev was replaced as commander of the First Army by general Dimitar Geshov. The Army itself exchanged headquarters with the Eleventh Army, now under the command of general Arnold von Winckler, and came under the new Army Group "Below", replacing Army Group "Mackensen" which was dissolved on the Macedonian Front on 30 July 1916 as field marshal Mackensen was needed in northern Bulgaria to take command of the forces concentrating for the operations against Romania. The former units of the First Army, now under German command, continued fighting around Monastir till December when the Allied offensive was finally halted. The new Bulgarian First Army now consisted of the Fifth "Danube" Infantry Division on the western bank of the Vardar, the Ninth "Pleven" Infantry Division between the Vardar and Lake Dojran, one brigade from the Eleventh "Macedonian" Infantry Division from Lake Dojran to the Belasica Mountain. For the rest of 1916 its sector saw only secondary fighting. On 21 April 1917 general Otto von Below was called to the Western Front and was replaced by general Friedrich von Scholtz who established a new army group bearing his name and composed of the Eleventh and First armies. During that time general Maurice Sarrail attempted a new offensive aiming to break the Macedonian front. The British were the first to attack the Ninth "Pleven" Division around Lake Dojran on 22 April. They were followed by the Serbians