Bosnia like his uncle Mladen I. George II Šubić and his son, Mladen III Šubić, ruled over Klis Fortress until the late 14th century. During summer-long festivities in Klis Fortress, open to the whole population, Mladen III Šubić gave his sister's Jelena Šubić hand in marriage to Vladislaus of Bosnia, from the House of Kotromanić. Jelena Šubić gave birth to the first Bosnian King, Tvrtko I, who later inherited the fortress. Petar Kružić and Uskoks Owing to its location, Klis Fortress was an important defensive position during the Ottoman conquest of the Balkans. The fortress stands along the route by which the Ottomans could penetrate the mountain barrier separating the coastal lowlands from around Split, from Turkish-held Bosnia. The Croat feudal lord Petar Kružić gathered together a garrison composed of Croat refugees, who used the base at Klis both to hold the Turks at bay, and to engage in marauding and piracy against coastal shipping. Although nominally accepting the sovereignty of the Habsburg king Ferdinand who had obtained the Croatian crown in 1527, Kružić and his freebooting Uskoks were a law unto themselves. When a large Turkish force threatened the fortress, Kružić appealed to Ferdinand I for help, but the Emperor's attention was diverted by a Turkish invasion into Slavonia. For more than two and half decades, Captain Kružić, also called (Prince of Klis), defended the fortress against the Turkish invasion. Kružić led the defense of Klis, and with his soldiers fought almost alone against the Ottomans, as they hurled army after army against the fortress. No troops would come from the Hungarian king, as they were defeated by the Ottomans at the Battle of Mohács in 1526, and the Venetians baulked at sending any help. Only the popes were willing to provide some men and money. Final Ottoman siege Pope Paul III claimed some rights in Klis, and in September, 1536, there was talk in the Curia of strengthening the defenses of the fortress. The Pope notified Ferdinand that he was willing to share the costs of maintaining a proper garrison in Klis. Ferdinand I did send aid to Klis and was apparently hopeful of holding the fortress, when the Turks again laid siege to it. Ferdinand I recruited men from Trieste and elsewhere in the Habsburg lands, and Pope Paul III sent soldiers from Ancona. There were about 3,000 infantry in the reinforcements, which made a sizeable relief