The Gardosh Fortress in Zemun, a unique and very important cultural monument, is a witness to great historical events. The fortress was built on a site from which navigation on the Danube was controlled for centuries, at the confluence of the Sava and the Danube rivers. On the site of the original fortress, the Romans built a castle in the 1st century and named it Taurunum, and in the 11th century a medieval fortress was built, the remains of which are still visible; it was destroyed at the end of the 11th century by the crusaders of the First Crusade. Throughout its turbulent history, the fortress was occupied by the Huns, Sarmatians, Goths, Avars, Franks, Slavs, Bulgarians, Byzantines, and Hungarians.

In the first half of the twelfth century, it is often mentioned in connection with the Byzantine-Hungarian wars, and the Byzantine chronicler Jovan Kinam claims that in 1127 the Hungarians captured the Belgrade fortress and built the Zemun Fortress from its stones. Later, Manuel I Komnenos (1143–1180) occupied Zemun and destroyed it (in 1151), transporting its stones across the Sava to rebuild Belgrade.

However, at the end of the 14th century, the Ottomans captured and destroyed both fortresses, Zemun and Belgrade. The famous Battle of Belgrade in 1456 was significant not only for Belgrade but also for Zemun. On the right bank of the Danube, the Christian army was led by Janko of Sibiu, that is, John Hunyadi, who managed to defeat the Ottomans and secure the peaceful southeastern borders of Hungary for the next 70 years. Just three weeks after the battle ended, while the victory celebrations were still ongoing, John Hunyadi died of the plague in one of the towers of the Gardosh fortress.

The Ottomans again destroyed the fortress in 1397, as well as the nearby Belgrade fortress. In 1411, the Hungarian King Sigismund of Luxembourg (1387–1437) handed Zemun over to Despot Stefan Lazarević (Prince 1389–1403, Despot 1403–1427), and in 1441 it was transferred to Đurađ Branković (1427–1456). On the right bank of the Danube, the Christian army was led by Janko of Sibiu, that is, John Hunyadi, who managed to defeat the Ottomans and secure the peaceful southeastern borders of Hungary for the next 70 years. Just three weeks after the battle ended, while the victory celebrations were still ongoing, John Hunyadi died of the plague (or from wounds according to other sources) in one of the towers of the Gardosh fortress.

During the Ottoman siege of Belgrade in 1521, they also besieged Zemun, which was captured on July 12 after strong resistance from its defenders led by Marko Skoblić. The fortress itself is mentioned in 1609, and by the 18th century it was already in ruins.

In the center of the fortress, at the end of the 19th century, the Millennium Tower was built, which today dominates Gardosh, and at the foot of the fortress is the oldest church in the city of Belgrade – the Nikola Church from the mid-19th century. The tower is named after the loess hill Gardosh in the eponymous settlement of Zemun. For the residents of Zemun, this is Janko Sibinjanin Kula, the Hungarian knight and fighter against the Ottomans John Hunyadi.

The people of Zemun did not forget their great hero and named the tower where he ended his life the Sibinjanin Janko Tower. It was the Hungarians, as part of the celebration of the millennium of the presence and rule of the Hungarians in this part of Europe, who built a monumental square in Budapest with two monuments in Hungary and Slovakia and four identical towers in four cities, on all four cardinal points and at the extreme borders of their country at that time. Thus, Zemun, as the southernmost city under the Hungarian crown, became the place where the Millennium Tower was built on Gardosh.

The tower is a mixture of different styles and is 36 meters high. During the construction of the tower, a small park was laid out around the tower and inside the fortress, which until 1914 was a pleasant walk for the residents of Zemun, offering a beautiful view of the Lower Town and the Great War Island. At the beginning of World War I, the Millennium Monument was damaged when Austro-Hungarian soldiers used it as a machine gun nest. Many mysterious stories have been told about the foundation of the tower. One such legend says that a tunnel leads from the tower's basement under the Danube to the fortress at Kalemegdan.

Today, the Gardosh Tower has been restored and is under the protection of the Institute for the Protection of Monuments of the Republic of Serbia.

Sources:

https://sr.wikipedia.org/sr-ec/Земунска_тврђава

https://tvrdjavesrbije.rs/zemunska-tvrdjava-gardos/