Built in the 16th century to defend the port of Sibenik from Turkish attack by sea, St. Nicholas Fortress (Tvrdava Sv. Nikole) is another of the five fortresses in the town and one of only three such forts still in existence in the Mediterranean (the others are in Venice and Malta). 

The fortress resembles an arrowhead and was built on the site of a former monastery, on a small island off the mainland. It was designed by the leading Venetian architect Hyeronimus di San Michaela and once boasted an impressive arsenal of 32 cannons.