The Burg of Ostrovica consists of at least three recognizable historical layers.
The medieval layer of the burg is built in 15th century upon the pre-historic gradina (fortified site), whose fortification walls remnants are partially preserved. It was built on the Ostrovica hill. The gradina was protected by a combination of a protective walls and steep rocks on the unapproachable South-east side. Its 282 meters long and 211 meters wide bunks are still recognizable. Underneath the western wall there was a ditch. On the west side there are ruins of 14 x 6 meter-building fundaments. The entrance is on the west side. This site is called Ostrovačka (also Grčka – Greek) crkvina.
The medieval burg of Ostrovica was a part of the Parish of Lapac and it belonged to the family of Karlović. In the Middle Ages that was the most strongly fortified burg in the upper flow of the Una river. Its growth continued during the Ottoman rule over Bosnia and Herzegovina. The main entrance was from the south and auxiliary from the north side of the burg.
In December 1523 the burg was taken over by the Ottoman armies and it remained in their possession until 1878 when it was abandoned. The importance of the burg is showcased by the fact that in 16th century the burg housed the crew of 60 cavalrymen and 150 infantrymen. In the 18th century the burg was further improved and fortified by four new towers and two fortresses and that was the final stage of its growth. The whole captaincy Stara Ostrovica (The Old Ostrovica) was named after this burg. The captaincy spread on both sides of the upper flow of the Una river, from its source to app. 15 kilometres down of what today is Kulen Vakuf. It included the burgs of Orašac, Havala,Džisir-kebir, Čovka palanka and Donji Lapac. Captaincies were organised in order to defend outer borders and protect inner territory, important roads and passes and later they also conducted police duties. The head of a captaincy was a captain and that was a hereditary office. After the peace treaty of Karlovac, the captaincy of Stara Ostrovica was significantly expanded and further fortified, and next to the Orašac burg a small town emerged. Also Havala and Džisir-kibir (The Large Bridge), today Kulen Vakuf came into existence.
The Captaincy was first recorded in 1699, with the family of Kulenović (also Haračlije) being the captains. At the front side of the burg, by the entrance, there was a Captain’s court (odžak).
The captaincy of Stara Ostrovica lasted until 1791. After the fall of Lapac, and with borders moving in the close vicinity of Stara Ostrovica, the captain moved his seat to Prkosi, where a new odžak and tower were built.
The first recorded captain was Salih-aga Kulenović and the last Mehmed-bey (period of captaincy 1821-1835).