For centuries, on the Mlađevac hill above Drina, the fortress has been countinuosly built. The legend says that cursed Jerina, the wife of the Serbian despot Đurđa Branković, built it and the famous dervish, Shaykh Hasan Kaimi also lived there. The fortress is known as Kula Grad or Đurđev Grad. It was one of the largest and most preserved medieval fortifications of Bosnia and Herzegovina.
There are assumptions that in the same place the Roman city Ad Drinum existed. Today, in the ruins on the surface of 49,000 square meters Gornji, Srednji and Donji Grad are identified.
The first tower that was built in the architectural ensemble of the Old Zvornik Town is Velika Kula in the central part of the fort. Initially it was a typical medieval complex with a rectangular tower and a small stagnation around it. Massive walls up to two meters thick surround the courtyard of the tower. The tower is made of stone from the surrounding area. The core of the wall makes a mixture of broken stone and mortar. The upper part of the tower, in the height of 4 to 7 meters, was added later.
At the very top, on the northeast sides, there is a window opening with a semicircular ending. On the west side of the tower, the remains of a similar opening are visible. There are four consoles in the vicinity of the hole that were carrying an extension, and the rest of the loophole that was used to control the entrance to the tower. Below the console, in a horizontal row, metal hoops, like cannon tubes, are used for unknown purposes.
A new way of warfare, the use of firearms and the need to protect this complex better from the northwestern side caused the development of Gornji Grad. This part of the city lies on a plateau surrounded by a high wall. At the top of the plateau, a main defense shield was built, which probably had one tower. On the east side of the plateau, in the most dominant place, there was a bastion or one of the towers mentioned in the report of King Matthias. From the south side of this bastion, the path led to Velika Kula. The bastions used to stand on more accessible sides of the plateau, but only the southern ones were preserved. In this form, the city stood until 1433, when it was occupied by despot Đurađ Branković.
The importance of Zvornik as a border town became emphasized in the Ottoman period, when the city was further established and expanded.
The lower town occupied an area of 7,600 square meters. Along the Drina River, in the first years of the Ottoman administration, an octagonal tower was built. The tower has been covered up to eight meters in depth. At the top, there is a room with five cannon holes and a fireplace.
In the 17th and 18th centuries, the fort has a more modern look. New materials and construction techniques were used to construct new buildings. In the lower town, at the site of earlier gates, towers (kapi-kula) were first built.
The northern entrance to the city led below the tower gate. Tower is a massive one-story object of a square base. Through the ground floor one could reach the entrance to the city, and on the first floor there was a room that had a cannon hole in the north, and in the south entrance to the room where it was possible to enter only with the use of ladder. In the interior of Gornji Grad, a large number of facilities for housing, offices and warehouses were built, as well as one smaller mosque. According to Evliya Çelebi, it was an “antique mosque, covered with lead and a dome-shaped attic. Above the front door, there was an inscription: “The benefactor, the Mighty Conqueror, has erected this mosque for pious people.”“
Austro-Hungarian period is characterized by interventions that are mainly related to demolition of the Old Town buildings, and to a lesser extent to construction. The caravan road in Donji Grad no longer satisfied the increased intensity of traffic, resulting in smaller interventions at the northern gate, closing the southern gate and the break-through for the new road. In Gornji Grad, Austria has built a barracks for the needs of its army. The building had a cellar with tanks, ground floor and first floor. The entrance was on the east side. The outer staircase led to the upper floor. On the north side there was a bunker and above its entrance there is a signboard plate today.
After the end of the First World War, further interventions are carried out on the expansion of the road. The passage through the northern gate is expanding, it significantly embedded the inner city o, raised the level of the road and almost completely demolished the southern gate. These works significantly devastated Donji Grad and the Old Town of Zvornik as a whole.