Hrvatska Kostajnica, often just Kostajnica, is a small town in central Croatia. It is located on the Una river in the Sisak-Moslavina county, south of Petrinja and Sisak and across the river from Bosanska Kostajnica in Bosnia and Herzegovina. Kostajnica was first mentioned in the document by knights templar from 1240. This year is used as official birth year of this historic town.
Time of the first settlement is unknown, but town lies on very important Roman roads that were used for transporting salt and cotton. Since Roman roads were merged in the vicinity of the city it is believed that settlement dates much earlier than the first written document known today. Position of town is very similar to the town from old roman documents known as “Oeneum”. Five roman milestones were located in the city dating back to the 3rd century A.D.
During 13th and 14th century Kostajnica became a fortification (kaštel) that was built as a protection against invading Turks. The owners of the fortification were members of the noble families Lipovečki, Tot, Frankopan, Benvenjud and finally Zrinski, so the castle is today known as Zrinski castle (Stari Grad Zrinski in Croatian). Other forts existing during that period were in the surrounding villages of Komogovina, Svinica, and Prevršac. The Turks invaded Kostajnica in 1556 and it wasn't until 1687 that the town was liberated.