St. Nicholas Fortress was built on the left side at the entrance of the St. Anthony (Sv. Ante) channel, on the island called Ljuljevac, in front of the Šibenik port. St. Nicholas Fortress got its name from the Benedictine Monastery of St. Nicholas, which was on the island, but due to construction of the fortress 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 an island of Ljuljevac in 30th April of 1525. 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 cannon. However, its imposing appearance and size were biger threat to enemy than canons.

The fortress is one of the most valuable and best preserved examples of defense architecture in Dalmatia. The fortress is made of brick because this material was considered to be most resistant to cannon balls, 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 made necessary because of the development of arms. It was completely abandoned by the military in 1979 and has been in renovation ever since.