This was due to fears that should Greece fail to participate in a future war against the Ottomans it would be unable to capture the Greek majority areas of Macedonia. The treaty was signed on 15 July 1912, with the two countries agreeing to assist each other in case of a defensive war and to safeguard the rights of Christian populations in Ottoman-held Macedonia, thus joining the loose Balkan League alliance with Serbia, Montenegro and Bulgaria. Fearing a new war in the Balkans, the Ottomans mobilized their armed forces on 14 September and began transferring units to Thrace; the Balkan League responded in kind. On 30 September, the League presented the Ottomans with a list of demands regarding the rights of its Christian population. The Ottoman Empire rebuffed the demands, recalled its ambassadors in Sofia, Belgrade and Athens and expelled the League's negotiators on 4 October. The League declared war against the Ottomans, while Montenegro had already began military operations on 25 September. Greece dispatched the Army of Epirus and the Army of Thessaly to its frontiers in Epirus and Thessaly respectively. The Army of Epirus numbered 20,000 men and 30 artillery pieces and was commanded by Lieutenant General Konstantinos Sapountzakis. Facing the Greeks in Epirus was the Yanya Corps under General Esad Pasha, which numbered 35,000 men and 102 artillery pieces; most of which were concentrated at the Yanya Fortified Area. The Army of Epirus was to conduct only a limited number of offensive operations, mainly focusing on protecting the Army of Thessaly's western flank. As it was too small to breach the Ottoman defenses around Yanya. The Yanya Fortified Area included two major fortresses, those of Bizani and Kastritsa, guarding the main southern approaches, along with five smaller forts in a ring around the city, covering the western and northwestern approaches. The terrain south of Yanya provided excellent defensive ground, as all the roads leading to the city could be observed from Bizani. The Ottomans had augmented their defenses with permanent fortifications, constructed under the guidance of German General Rüdiger von der Goltz. These were equipped with concrete artillery emplacements, bunkers, trenches, barbed wire, searchlights and machine gun positions. The Army of Epirus crossed the bridge of Arta into Ottoman territory at midday 6 October, capturing the Gribovo heights by the end of the day.