Ali pasha started from Adrianople in the spring of 1388 with thirty thousand men to complete the conquest of Bulgaria. He crossed the Balkans by the pass north of Aïtos, which has ever since been called by the Osmanlis Nadir Derbend from the neighbouring town of Nadirkeuy.[407] Provadia was taken by surprise in the night. Shuman and the villages around it were next conquered. After an unsuccessful attack upon Varna, the Osmanlis retraced their steps through Provadia and Shuman, following the line of the modern railway from Varna to Sofia. Tirnovo, the ancient capital of Bulgaria, capitulated after a short struggle. Sisman withdrew to the Danube through the valley of the Osma, and shut himself up in the fortress of Nicopolis. Owing to the ease of provisioning from the river side, it was impossible to starve him out. Ali pasha was compelled to call upon Murad, who had just crossed over from Asia to Thrace. When Murad arrived before Nicopolis, Sisman sued for peace. The conditions of Murad, that he pay the tribute due from the previous year and allow an Ottoman garrison to occupy the fortress of Drster as gage of future good conduct, were gladly accepted. No sooner had Murad started southward than Sisman decided upon a final desperate resistance. He refused to give up Drster. But he had forgotten that Ali pasha was master of Shuman and the route to Varna. The Osmanlis took Drster by storm. Many villages along the Danube between Rustuk and Nicopolis fell into the hands of the Osmanlis. Ali pasha besieged Sisman for a second time in Nicopolis. The revelation of his own weakness and of the strength of the Osmanlis was a crushing blow to Sisman. He surrendered without conditions, and was taken, with his wife and children, to Murad’s camp. For reasons which the chroniclers do not indicate, Sisman was able to secure forgiveness and restoration to his former position as vassal prince of Bulgaria. But the Osmanlis were now installed in north-central Bulgaria up to the Danube River. Shuman and Nicopolis were Ottoman fortresses. Sisman had been rendered impotent to give effective aid in the great alliance.[408] XVII Not all the Christians were loyal to the cause of Balkan freedom. In their conquest of the Balkan peninsula, it is remarkable that the Osmanlis never fought a battle without the help of allies of the faith and blood of those whom they were putting under the Moslem yoke. At the beginning of this chapter, it has been shown that there is no historical basis for the assertion that the Osmanlis conquered the Balkan states by the use of the janissaries. But they did have Christian aid of a far more powerful kind than the janissaries could have given them. The old fiction of the janissaries won for the Balkan people the sympathies of western Europe. The truth concerning the Christian aid which the Moslem conquerors received alienates rather than wins our sympathies.