St. Nicholas' Fortress was built on the left side at the entrance to St. Anthony Channel, on the island called Ljuljevac. The island is situated at the entrance to the Šibenik channel across the Jadrija beach lighthouse. St. Nicholas' Fortress got its name from the Benedictine Monastery of St. Nicholas, which was originally on the island, but due to the construction of the fortress, it had to be demolished. At the request of domestic Croat population of Šibenik, the Venetian captain Alojzije de Canal decided to build a fort on the island of Ljuljevac in 1525. The fortress was designed and built by the famous Venetian architect and builder Hyeronimus di San Michaela. It was built by in the 16th century to prevent Turkish boats from reaching the port. St. Nicholas' Fortress was armed with 32 cannons. However, its imposing appearance and size were a bigger threat to the enemy than cannons ever were.
The fortress is one of the most valuable and best preserved examples of defense architecture in Dalmatia. It is made of brick because that material was considered to be most resistant to cannonballs, while the foundations are made of stone. Although defense capabilities of the fortress have never been tested in military operations, the structure still proved successful in protecting the city from sea-bound enemy attacks. During the centuries of use, the structure served to various armies and has undergone a number of renovations, some of them necessary only because of the development of arms. It was completely abandoned by the military in 1979 and has been undergoing renovation ever since.
St. Nicholas' Fortress was included in UNESCO's World Heritage Site list as part of 'Venetian Works of Defence between 15th and 17th centuries' in 2017. After reconstruction work that lasted for two years, the fortress was open to visitors in July 2019.
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.