Frankopan Castle Krk was built over several centuries by the Croatian princes of the Frankopan family. The oldest part of the complex is the Square Tower founded in the 12th century - originally a belfry and observation tower, then the seat of the court, and now a place for the presentation of the exhibition dedicated to the history of the Frankopans. In the 13th century a round Venetian Tower was added. The youngest, dated to the fourteenth century, is the Austrian Tower.
The castle was an important part of the city's fortifications. Its simultaneously representative and defensive character is evidenced by walls erected from hewn stone, whose thickness reaches up to 2 m. It is not known when exactly the construction was completed - it is certain that Frankopan Castle was built before 1348.
At the end of the twelfth century among the many powerful nobles that lived
the island of Krk, the Frankopan family began to dominate. The first Ukrainian (prince) was Dujam I Krčki, who in 1118 declared himself a sovereign ruler. In the following centuries, his successors concentrated their power on a territory equal to half of today's Croatia.