In Tutrakan the citizens allowed the Turks to install a small garrison but then they killed the Turkish soldiers and prepared for siege. Ali Pasha immediately burned the surrounding fields and soon the starving town had to surrender. After this success they advanced to the west towards Nicopolis, one of the strongest Bulgarian fortresses along the Danube. The defence was organized by Ivan Shishman who was currently in the town. Although the Ottomans had nearly 30,000 men they could not take it and Ali Pasha had to seek reinforcements from Murad himself. According to Seadeddin the Sultan marched to Nikopol with an enormous army firmly decided to seize the town at all costs. When Ivan Shishman faced the new enemy he sought a truce. Murad agreed and the Bulgarians saved Nikopol but were forced to cede another key Danubian fortress, Dorostolon. However, when Ali Pasha reached Silistra, the Bulgarians refused to surrender the town. Murad besieged Nikopol for a second time and this time Ivan Shishman agreed to the Ottoman conditions and a Turkish garrison was installed in Silistra.