The fortress in Tešanj is one of the largest and most significant facilities of its type in Bosnia and Herzegovina.
The Old Town Tešanj or Gradina was built on a hill in the valley, along the Tešanjka River, on a steep and partially cut-off cliff of the hill, hard to access from three sides.
This fortified settlement from the medieval period was constructed on the top of a rocky hill. It consists of a polygonal tower and walled yard.
The yard had the shape of an irregular semicircle, with a radius of some 26 meters. On the northeastern side of the yard there was a twelve-angled tower which is presumed to be originally high between 15 and 20 meters, with a ground floor and three more floors.
This tower was the main point of defense of the medieval town.
The yard once had wooden residential facilities and one well, which is buried now. It was buried by the Germans in the Second World War, after they searched it in detail.
A small, protruded heptagonal tower was built near the big one. That was the original construction of the first town of Tešanj from the medieval times. In early 15th century the town changed its form and turned from a medieval castle into a fortress.
On the top of the hill walls were built, thus completely closing the defense system. When they conquered the town in 1520, the Ottomans found only ashes and destroyed towers.
In late 17th century, the Ottomans reconstructed the city. Then they added a new part to the Tešanj town, the lower part of the town.
Military troops left the old town of Tešanj in 1840.