Zrin Fortress is a medieval fortress located on the slopes of Zrinska Gora above the present-day Zrin village of the same name, fifteen kilometers north of Dvor, today's municipal seat. In the Middle Ages, Zrin was a very important property of the Zrinski family, the center of a large territory along the left bank of the Una, from Kostajnica to Žirovac and to the peaks of Zrinska Gora.
The first written sources about the town of Zrin date back to 1295, as the place where Stjepan II. Babonić, the owner of these regions, wrote a gift deed. And in 1302, Zrin was the place where the grant was written. Zrin must have been one of the seats of the Babonić family, which at that time held part of today's Banovina and the Bosnian Krajina. However, the Babonići did not hold Zrin for long. In 1347, King Louis I of Anjou took Zrin from Lovri Tota, the prefect of the Vašvar and Sopron counties[1] and gave it to Gregory IV. and his protégé George III. Bribirsko, in exchange for Ostrovica near Zadar. George III. Bribirski thus becomes the founder of the Zrinski family as Juraj I. Zrinski. Since then, the Zrinskis gradually spread their possessions to the area between the upper Una and Kupa, so in the late 14th century they already occupied larger parts of today's Banovina and Kordun.
The Zrinski gained economic power in the middle of the 15th century, when King Matthias Corvin allowed them to exploit the silver and lead mines in Gvozdanski. Nicholas III. Zrinski later started minting money in the area of Gvozdanski. The danger of the Ottomans in these areas was felt only after the fall of Bosnia in 1463.
In 1493, the head of the Zrinski family, Petar II, died in the battle with the Turks on Krbavsko polje. Zrinski, and is succeeded by his son, the underage Nikola III. Zrinski, who already founded a Franciscan monastery in Zrina in 1504, of which only the chapel of St. Margaret in ruins has survived to this day. Until recently, on the western facade of the chapel stood the stone tombstone of Nicholas III.
In 1508, the most famous descendant of the Zrinski family, Nikola Šubić Zrinski, was born in Zrin, and the Zrinskis remained the owners of Zrin even after his death near Siget, until 1577, when it was conquered by the Turks.