St. John's Fortress

St. John's Fortress, locally known as Tvrđava svetog Ivana, lies in the town of Šibenik, in the county of Šibenik-Knin in Croatia.

For centuries before the construction of St. John's Fortress, the town of Šibenik was protected by city walls and St. Michael’s Fortress. However, by the 17th century, these defenses had become outdated and vulnerable. At that time, Šibenik was a Venetian possession.

The site of the fortress, a hill overlooking the town, had long been considered strategically important. As early as the 1520s, Venetian engineers warned that Šibenik was at risk if enemies seized the high ground. In 1646, during the Cretan War between Venice and the Ottoman Empire, this vulnerability became urgent. With the Ottoman front only 5 km away, the citizens of Šibenik decided to build a fortress at their own expense, with support from a Franciscan engineer, Antonio Leni. Construction began on August 1, 1646, and was completed in just 58 days.

A new redoubt was also built on a slightly lower hill nearby, known as Barone Fortress.

In October of the same year, St. John's Fortress withstood its first Ottoman attack. During the summer of 1647, it was again heavily besieged by an army of up to 30,000 soldiers. After intense shelling and ground assaults, the defenders repelled the enemy on September 8, forcing the Ottoman army to retreat days later.

The fortress was expanded over the following years. A series of hornworks replaced the original outer structures, and connections were made to Šibenik’s other fortifications. It remained in military use into the 18th century but lost strategic importance after the Ottoman threat diminished.

Throughout the 20th century, the site fell into neglect. Sports courts, antennas, and other modern installations were added within the ruins. In the 2010s, a major revitalization project began. Archaeological excavations uncovered original walls from Leni’s 1646 design. Restoration work followed, financed by the City of Šibenik and the European Union.

Today, St. John’s Fortress has reopened to visitors. It offers historical interpretation, walking paths, and spectacular panoramic views of Šibenik and the Adriatic coast, a remarkable fortification.

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