On a prominent elevation on the right bank of the Danube, above the present-day village of Stari Slankamen, lie the remains of a medieval fortress built on the foundation of a Roman castle. This area has been densely populated since prehistoric times, and during the Roman administration, a fortification called Acumincum was built here. Throughout history, it was conquered by many peoples: Huns, Goths, Gepids, Avars, Bulgarians, Byzantines, Hungarians, and Turks. The medieval town of Slankamen is first mentioned in historical sources in the 11th century. In later periods, its names included Zalonkemen, Zolankaman, and Zolankament. At the end of the 12th century, Slankamen was seized from the Byzantines by the Hungarians. By the early 14th century, it had gained the status and privileges of a royal city (Civitas regis Zalankaman). According to sources, it can be concluded that a class of wealthy merchants and craftsmen developed in Slankamen quite early.

With the strengthening of Turkey in the 15th century, Hungarian kings began granting many of their estates to Serbian nobility as feudal holdings on the condition that they would defend them. Due to its important position controlling navigation on the Danube and the mouth of the Tisa, in the 15th and early 16th centuries, Slankamen was a very important point in the defensive system of southern Hungary and the most important center of the boat fleet along the entire Danube. In 1504, there were about 500 boats in Slankamen, and in the 16th century, there was even a shipyard for warboats. These were light and fast wooden vessels propelled by oars or sails. They were very maneuverable, equipped with a cannon on top, and used both for attack and defense. The first Serbian ruler to own Slankamen was Đurađ Branković. Then, according to sources, control passed to King Sigismund. After the war and subsequent truce with the Hunyadi family, it was decided that he would transfer Slankamen and other towns of Srem to them. The strategic importance of this place is also shown by the fact that the army and boat fleet gathered here during the defense of Belgrade in 1456. The fortress returned to direct royal control in 1502, and two years later, 500 settlers lived there under the leadership of two princes.

Immediately before the Turks captured Belgrade (1521), representatives of all the nobility went to Buda to request their salaries, and when they did not receive them, they abandoned service. This greatly weakened the army since the boat fleet was one of the main forces in the previous defense of Slankamen, so it can be assumed that its absence undoubtedly contributed to the quicker capture of the city by the Turks. The city fell almost without a fight in 1521. Along with many fortresses of Srem, it was burned to create a wide strip of desert and no-man’s land that could in no way serve the enemy army coming to liberate Belgrade. In the years following the decisive Battle of Mohács (1526), a significant part of Hungary became part of the Ottoman Empire and remained so for the next 175 years.

In 1691, the Turks suffered a severe defeat near Slankamen and subsequently lost this city along with large territories. According to reports received immediately afterward, the city was already in ruins.

Since Slankamen was no longer a border fortress, it lost its military significance and began to transform into a typical Turkish town of that period. The fortress (upper town) housed a garrison but was no longer an important fortification. In the lower town, trade, viticulture, fishing, and crafts flourished. Slankamen belonged to the Srem Sanjak and was the residence of a nahija chief. During the Great Turkish War, when the Habsburgs managed to defeat the Ottomans and take control of this territory, one of the decisive battles took place near Slankamen in 1691. Today, only a few walls remain of this once imposing fortress.

We have few detailed descriptions of medieval Slankamen. The fortress foundation has an irregular circular shape. The fortress was divided into well-fortified Lower and Upper towns. The bricks were made of very low-quality sandstone, with some Roman bricks found in places. On the somewhat better-preserved eastern wall, remnants of two towers can be seen, one rectangular and the other semicircular; only the foundations remain of the other walls. During the Turkish invasion of these areas, there were probably five towers. The official census of 1702 describes some buildings: three churches—two ruined Catholic and one Orthodox—a well-built Turkish bath, a mosque, and several larger buildings.

Today, the remains of the upper town and one of the towers have been preserved here.

Sources:

https://sr.wikipedia.org/sr-ec/Сланкамен_(тврђава)

https://zavodsm.rs/tvrdjava-stari-slankamen/