Gradačac Castle has a fort with walls 18 metres high, built between 1765 and 1821, and a watchtower 22 metres high, built in 1824 by Husein-kapetan Gradaščević on foundations made originally by the Romans. It is finished in the 19th century. In 1831 general rallied the Bosnians against the Turkish occupation and drove the Ottomans out to Kosovo, winning Bosnia its sovereignty for the coming year. Therefore, fortification has great historic importance for Bosnians. It has been recently renovated.
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.