Klis Fortress is one of the most complete examples of fortification architecture in Croatia. It is located at a strategically important position in the locality bearing the same name of Klis in the Split-Dalmatia County, right on the pass between Kozjak on the west side and Mosor on the east side. Due to its strategic position at the crossing from Split to Zagorje and Bosnia, battles for supremacy were fought in that area for centuries. Klis Fortress represents one of the most prominent fortresses in Croatia, and mentioned for the first time in the 5th century. It deserves its fame mostly from the time of the Turkish wars, when the captain of the Fort Petar Kružić and his Uskoks resisted attempts at Turkish conquest for decades, until it fell into Turkish hands in 1537. Until then, Klis and its immediate surroundings remained the only free part of the Croatian Kingdom in the south, a real enclave. The Klis Pass is the most suitable point of communication between the central Dalmatian towns and the hinterland, which will gain additional importance during the Ottoman presence in these areas.
The migration of the Croats in this area is an undoubtedly important event in the past of Klis for two centuries later Klis Fortress as a royal estate was one of the centers of the Croatian state. In the 9th century, Klis was the seat of Croatian princes and kings from the Trpimirović dynasty, and in that capacity it was the Croatian capital. It later belonged to various Croatian feudal lords. When the Croatian national dynasty of Trpimirović died out at the end of the 11th century, Klis came under the rule of Hungarian-Croatian kings who often handed it over to the administration of their princes and bans. At the beginning of the 1920s and 1930s, the Croatian nobleman Domald managed to take over Klis, but both times the Šubićs took it away from him and returned it to the king's rule.
Due to its prominent position, it was a difficult fortress to conquer for a long time. Medieval Klis was the seat of the Uskoks, Croatian fighters against the Turkish and Venetian invasion. In conquering it in 1537, the Turks succeeded in taking over Solin and penetrate through the Kaštel localities on the southern flanks of the Kozjak but they never succeeded in taking over Split. The Turks fortified it and built a mosque with a minaret. During their rule, it was the seat of the administrative unit of the Klis Sandžak. The remaining Klis Uskoks, after the fall of the fortress, moved to Senj (Senj Uskoks).
Klis was freed for a brief period in 1596, but finally in 1648, during the Candian War, it was conquered by the Venetians. They fortified it and turned the mosque into a church. Present day Klis derives from the time of the last Venetian reconstruction. The newer settlement appeared after the withdrawal of the Turks. There is an old Turkish fountain in the locality. The historical collection from the Fortress was moved to the Museum of the City of Split.
The Fortress
The fortress was erected on a rocky gorge that extends in northeast-southwest direction and it is almost impossible to discern the structure, all the more so as the walls that cascade up in three belts are built of limestone blocks on limestone rocks. It is inaccessible from as many as three sides - the only access is on the northwest side. The north side is exceptionally steep, while the southern side is of somewhat milder descent. These features definitely influenced numerous unsuccessful attempts of conquering the fortress. The key position for cannon attacks was Greben, high ground to the north of the fortress. The floor plan of the fortification was elongated and narrow, which led to the upgrading destroying part of the earlier layers. In ancient times, an Illyrian hillfort existed on the site of the fort. Most of its present appearance derives from the Venetian and Austrian administration period when the fortress was modernized. During the Ottoman period, there were no alterations to the fortifications. The parts of the fort dating from the period of Ottoman rule (1536-1648) are the mosque, today the church of St. Vitus, and the fountain.
The Mosque
The mosque is located inside the third defense wall between bastions Bembo and Malipiero built during the Venetian administration period. It has a square floor plan and small dimensions because it was intended exclusively for the crew of the fort. It was built directly after the fall of Klis in 1537. The mosque bore the name of the conqueror of Klis, Murat-bega Tardića. Tradition was that mosques were named either after the ruling sultan (in the Croatian area, therefore, they mostly bore the name of Suleiman the Magnificent) or after the person who financed and initiated the building of the mosque as was the case in Klis. Recent research indicated that on that same place earlier stood the early medieval church of St. Mary. The mosque was built of untreated stone, vaulted with a dome, and a very interesting solution is the transition from a square floor plan to a circular base of the dome with a double tambour - first octagonal with four spacious, somewhat clumsily executed trumpets, and then a ring tambour. On the trumpets, we encounter an interesting decorative element called mukarna - a typical oriental decorative element that is regularly used to fill spherical surfaces - domes, calottes, trumpets, etc. Here they are applied in a significantly reduced form. Interestingly, with the later conversion into a church the mukarnas were not removed. However, with the necessary change in the orientation of the church, the old entrance to the mosque was walled up, and a new one was opened on the south-west side. The minaret on the western side was taken down and quarters for Venetian officers were built of which on the foundations have been preserved. An interesting inscription is on the site of a former minaret niche, i.e .above today's entrance: “What piety builds, piety also preserves”. The manner of expression of the architecture and the execution of certain constructive and decorative elements lead us to conclude that this building is by no means a top architectural achievement. Finally, its function-dependent dimensions but also the location within the defensive fortification justify this. The mosque, i.e. the church of St. Vidius, has recently been restored.
The Fountain
Another preserved object is the fountain between Greben and Klis, at the foot of the fortress, which is used even today. The locals call this fountain The Three Kings. That name was already mentioned in the 17th century on Eraut's depiction of the fortress as Fontana dei Tre Regi.[3] The cistern is built of stone blocks with an open porch and an oriental vault with pointed arches. It belongs to the „mihrab fountain“ type – a fountain with a niche. This is not the only example of a Turkish fountain in Croatia. A large number has been preserved and most of them are still in use. Water supply was the basic need of the Islamic community, and important for their religious practice. Water has an essential role in Islamic religious rites. Prayer is always preceded by ablution - a religious cleansing that uses water. The Shariah regulations of Fiqh describe as many as four types of water and eight types of impurities. However, water supply also played an extremely important practical role during long sieges. Loss of water (and food) would generally mean forced surrender. In addition to the fountain at the foot of the fort, there were several other cisterns that were built as needed.