On the morning of September 14, 500 guns opened up along the mountains and ravines between Monastir and the Vardar.
The Germans were amazed at this concentration of firepower which, although slight by the standards of the Western Front, approached a ferocity unknown in the Balkan zone of operations … Yet, although surprised by this dramatic opening of the offensive, Scholtz’s staff [General von Scholtz – a distinguished veteran of Tannenberg – was the commander of Army Group von Scholtz and located in Skopje over 60 miles away] were not unduly disturbed by the news which reached them. While the bombardment was at its height the Germans gave orders for a Bulgarian regiment and a Saxon Jäger battalion to be sent from Prilep to cover the slopes north of Monastir, where it was assumed the French would attack as soon as the bombardment died down. This region was more than 20 miles west of the Dobropolje and it was only after dark on September 14 … that [Scholtz] realised where the main assault would come. By then it was too late for counter action; and in the initial fighting the Bulgars and Germans in this sector remained outnumbered by three to one.
From ‘Defeat of Bulgaria – The Central Powers Begin to Crack’ by Alan Palmer, published in History of the First World War No. 107 by Purnell for BPC Publishing Ltd, London, in cooperation with the Imperial War Museum.
This map, from the British Official History of the Macedonian Campaign (Vol. 2) published in 1935 (but reprinted in various editions since), shows the planned allied assaults; that by the First and Second Serbian Armies on 15 September and the later secondary attacks, including those by British and Greek forces at Doiran.