The Ottomans under the leadership of Ahmed Pasha conquered the fortress of Šabac on 7 July in 1521.[1][2][3] All of its defenders were killed.[1] After its conquest Suleiman said that it was one of the cities he had conquered and that it must be improved.[1] He ordered towers to be built around the fortress and a moat around it filled with water from Sava.[1] Suleiman spent 10 full days on the Sava at Šabac overseeing the construction of the pontoon bridge.[1]