According to chronicles, the Avar fortress, which existed in 873 in Bač, predated the later fort.[1] It was inhabited by both Avars and Slavs. The Hungarian King Stephen I founded Bács County, and at the turn of the first millennium Bač (Hungarian: Bács) was already a well built and fortified town, connected to the Danube by the river Mostonga. During the Árpád dynasty, Bač became not only the ecclesiastical seat of the Archdiocese of Kalocsa, but a royal city, where nobles and rulers came to their councils and assemblies. In the twelfth century Bač fortress is first mentioned in written sources.

At the head of Bács county there were ispáns appointed by the king. Until the Mongol invasion in 1241, the ispáns were the managers of the area. They collected donations, set up military and civilian commanders. In addition to the governors of the fort there were also lower prefects, judges, and military personnel. Since the twelfth century, the custom of annual royal visits to the fort was established.

At the beginning of the fourteenth century a dynasty change occurred in the Kingdom of Hungary. and the town prospered during the rule of king Charles Robert I, who started building the modern fortress in 1338–42.[2] The new town (fortress) on Mostonga had the quadrangular tower with six floors, important for the defense of the city. Originally there were 8 towers, various chambers of the county manager, a chapel, guard towers, kitchen, water well, barn, and various other premises, the remains of which stand today.

The fort and the town developed as Bač was the major crossroad at the time. Roads from and to Europe, the Balkans and the Mediterranean all crossed here, and the tall central tower allowed the overseeing and control of the lowlands and both the river and the land traffic.[2]

Though the construction began in the first half of the 14th century, which is the base of what survived until today, the complex was shaped in the present way by the 15th century and reached its full extension by the 16th century. Archbishop Péter Váradi [hu] expanded and embellished the fortress and also dredged the Mostonga so that ships from the Danube were able to reach the fort.[2]

From the 15th century, it was the most important Hungarian defense point against the invading Ottoman forces. The pivotal moment was the disastrous Hungarian defeat in 1526 at the Battle of Mohács, so the Ottomans conquered Bač in 1529.[3] During the war between Ottoman Empire and the Kingdom of Hungary, in the 16th century, Serbian despot Stevan Berislavić successfully defended the Bač fortress from the Ottomans for a long time until the fortress finally fell.

In the aftermath of the Battle of Mohács from 1526, the city and fort became an Ottoman possession.[4] During the Ottoman rule (16th-17th century), Bač was the seat of the Kaza of Baç, as part of the Sanjak of Segedin. Dating from this period are also the descriptions of Bač Fortress by the Ottoman traveler Evliya Çelebi. According to his description, the city was surrounded by a wide circle of trenches filled with water. Surrounding the city was also a developing civilian settlement, which could be entered through the fortress drawbridge gate, named the "Spike".

Since 1686 the town was under Habsburg control. The fortress was mined with explosives in 1704, during the Rákóczi's War of Independence (1703–11),[3] and was subsequently abandoned as it was left burned, demolished, and without the previous military importance it had.[2] However, Bač fortress still remains the best preserved medieval fortress in Vojvodina.[1]

Serbian army entered Bač in November 1918. On 25 November 1918, the local assembly of Banat, Bačka and Baranja voted unification with Serbia, which, in turn, merged into the Kingdom of Serbs, Croats and Slovenes on 1 December 1918, renamed Yugoslavia in 1929. The area was occupied and annexed by Hungary in April 1941, during World War II, until 22 October 1944 when it was liberated by the Yugoslav Partisans and Red Army Since 2003, it was part of Serbia and Montenegro until 5 June 2006, when Serbia restored independence.