The fortress of Klis is one of the longest enduring fortress' held in isolation from the rest of the territory of the Kingdom of Croatia. The unwavering efforts from count and captain Petar Kružić was an essential factor of Klis defense against the constant siege attempts by the Ottomans. In addition to the active defense of Klis, it is necessary to emphasize the help of King Ferdinand I. Habsburg, as well as two Popes Clement VII. and Paul III. that took care for the Christian world. Under Klis in the 16th century, many Ottoman leaders failed in siege attempts, and Murat-bey Gajdić under the command from Gazi Husrev-bey was the one that succeeded. The fall of Klis is closely connected to the death of Petar Kružić in the attempt to break the siege, and the infamous defeat of the Habsburg relief army under the Solin fortress. After Kružić, there was no commander that could fill the vacancy. The fall of Klis by surrendering of the garrison forces after the most exhaustive siege (August 31, 1536- March 12, 1537) meant the completion of Ottoman conquest of the southern part of the territory of the Kingdom of Croatia.