Tržan Castle in Modruš The Tržan Castle ( ; or " Utvrda Tržan " ) is a ruined medieval castle situated above the village of Modruš in the northern part of historical Lika region , central Croatia . Before ( from the 11th century ) the administrative seat of the former Modruš County ( later renamed Modruš - Rijeka County ) , it is today just a ruin in the Josipdol Municipality in the southern part of the Karlovac County . Having been built on a ridge of a steep hill ( 670 metres above sea level ) on the eastern slopes of the Velika Kapela mountain , the castle was located on a strategic place overlooking the road that connected the Adriatic Sea and the Pannonian Basin since the ancient times , precisely the Roman towns of Senia ( present - day Senj ) and Siscia ( present - day Sisak , and which was later , during the 18th century , reconstructed and improved under the name of Josephina road . History . According to the famous Croatian historian Vjekoslav Klaić ( 1849 – 1928 ) , a kind of a castle or stronghold most probably existed above Modruš already at the beginning of the 9th century , during a war between Borna , Duke of Dalmatian Croatia , and Ljudevit Posavski , Duke of Pannonian Croatia . Almost ideal position , dominating over the surrounding area , made Tržan Castle never to be conquered by anyone in its history , although the town of Modruš below the castle was plundered and burned by the Ottomans in 1493 , just before the battle of Krbava Field . From 1193 the castle was property of the Knezes ( Princes ) of Krk , ( later , from around 1430 , known as the Frankopans ) , a distinguished Croatian noble family . Bartol II Krčki / Bartholomew II of Krk / was given the whole vast Modruš estate , including the castle , by the Croato - Hungarian king Bella II ( III ) for his merits in the wars he fought . The next more than 350 years Tržan was owned by the Frankopans , not only as one among the many castles in their property , but as the main seat and stronghold of the family in the whole continental part of Croatia . From thence ruled , among others , Ivan V Krčki / John V of Krk / ( born before 1343 , died 1393 ) and his son Nikola IV / Nicholas IV / ( born around 1360 , died 1432 ) , the most powerful man in Croatia at the beginning of the 15th century , both Bans ( Viceroys ) of Croatia . They reconstructed and enlarged the old , irregular shaped castle , which was from around 1437 called Tržan or Tržan - grad , because of an increased trade that was going on there ( ) . The walls , bastion s and towers were built of hewn stone ( ashlar ) in the „ fishbone “ style and represented a kind of masterpiece of the contemporary building skill . There are some signs which indicate that the foreign building masters took part in the works , most probably those from the Republic of Venice . The castle itself consisted of central part with a large guard tower and a palace as residence for members of the princely family with its supporting staff , northern part with outbuildings for economic services , various workshop s , warehouses , water tank s and rectangular defending tower , and southern part containing mostly facilities for retail trade , accommodation for traders and travellers etc . Following the walls and bastions of the castle , there were about 1200 meters long defensive wall s around the town of Modruš , descending the slope of the hill . In 1449 a well - known partition of the huge Frankopan estates , spread throughout central and western Croatia , took place , as the eight sons of Nikola IV Frankopan agreed to split and share their father ` s property ( legally valid ) among themselves . In the course of this , the whole Modruš estate belonged to Stjepan III / Stephen III / ( born before 1416 , died around 1481 / 84 ) ; in the sharing inheritance document it was written : „ . . . to Stjepan belongs the market town Modruš with the Tržan " Castrum " “ . . . It was a time of constant and steady rise , a „ golden age “ of Modruš , that reached its peak in 1460 , as the town became a seat of a bishop . Bernardin Frankopan ( 1453 - 1529 ) , the only son of Stjepan III , successfully managed the whole of his property further from the Tržan Castle , although there was increasing threat of the Ottoman raids from the already conquered Bosnian territory , east of Modruš County . This led to decrease of importance of Tržan by the end of the 15th century , and the population of the whole area started to move away more and more from its old places of residence to the other , safer parts of Croatia and neighbouring countries , not willing to live in endangered territory . In the first half of the 16th century the castle was always less maintained and repaired than needed , and after 1553 came under control of the military authorities of the Croatian Military Frontier . A relatively small military deployment unit was permanently stationed there . After several unsuccessful attempts to renovate or rebuild the more and more severely damaged parts of the castle during the 17th and 18th century , the military authorities decided in 1791 to abandon it . Following the negligible Ottoman danger at that time , they presumed that it was not necessary to keep soldiers in Tržan and it was left to its own destiny , becoming a badly damaged castle ruin today .