Šabac fortress (Serbian: Шабачка тврђава), also known as Bigir Delen in Turkish, is a fortress next to modern day Šabac, on the right riverbank of Sava.
The fortress was built in 1471 by Isa-Beg Ishaković, but soon afterwards, in 1476, it was conquered by the Hungarian army helped by Serbian despot Vuk Grgurević, who kept the Šabac fortress under his control for more than four decades. In 1521, on his campaign on the way to Belgrade, Suleiman the Magnificent conquered Šabac. As soon as he got hold of it, he had the earth palisade fortifications replaced with bulwark constructions with towers. In the period from 1717 until 1739, during temporary Austrian occupation, the fortress underwent significant adaptations and its surface was extended with additional construction of outer fortifications.
