There was, however, another route which the enemy had not thought of fortifying, relying on its formidable natural defences. Between the Cerna and Nonte there is a group of high peaks rising from a wilderness of rocks around a basin hidden among the mountains. The area is called the Moglena, and it is here that the Moglenitza river has its source. The mountains of this group are among the highest in Macedonia; several summits, such as Floka, Kaimakchalan, Dzena, are over 2,000 m., the Mala Rupa is over 1,900 m., Sokol, Dobropolje, Vetrenik, Kuchkov Kamen and Kravitza are about 1,700–1,800 m. In the offensive of the autumn of 1916 the Serbs had conquered the Kaimakchalan range and the Moglena area, which was afterwards entrusted to the II Serbian Army. Since then the sector had been a peaceful one, except for the engagements in the spring of 1917. Voivod Michich had repeatedly insisted on the advisability of an offensive against the Dobropolje, as offering the best chances of success. General Sarrail had refused to trust the man who knew far more about Balkan warfare than he did. General Guillaumat, on the other hand, believed the plan to be possible, and began the preliminary studies for an operation in that direction. But more and heavier artillery was needed than the Armée d’Orient as yet possessed. Guillaumat, therefore, only executed the attack on the Srka di Legen. To General Franchet d’Espérey is due the merit of having taken up the plan once more, perfected it and finally executed it. As a result of his inspections along the front, he convinced himself that while the vital ganglion of the whole enemy organization was the middle Vardar, an attack on any of the four traditional sectors was, with the means at his disposal, impossible. From Mount Floka he studied the conditions of the ground with minute attention, and realized that a surprise attack in the Moglena area might succeed, because the Bulgars were not likely to expect it. It was necessary to break through in the centre, and once the breach was made to spread out in a fan-like formation to reach Gradsko and Demir Kapu, thus cutting the enemy’s communications and separating the XI German Army from the I Bulgarian Army. At the same time powerful diversive actions on the right and left wings (Doiran sector and Cerna loop) would nail down the enemy and prevent them from sending reinforcements to the centre.