Ključica, the largest and most beautiful medieval fortress in the Krka River basin, and today the best preserved, was erected on an uneven, steep cliff on the bank of the Čikola River.
The medieval fortress called Ključica or Ključ is located on the right bank of the canyon of the Čikola River, a kilometre from its influx into the Krka River. It belonged to the system of fortifications that were built by the Croatian noble Nelipić family in the period when they ruled over the area of the Miljevci region. Ključica was mentioned directly for the first time in 1333, when the Venetian authorities demanded that Izan (Ivan) Nelipić of Ključ (comiti Ysano de Clavi) compensate the Šibenik district for the damage caused by his looting attacks, and that he release the captured citizens from Šibenik. After Ivan’s death, Ključica for some time remained the seat of his son, Konstantin, who was mentioned in 1337 as the prince of Ključ (Constantino comiti Cluci). In the first half of the 14th century, the forces from Šibenik succeeded in breeching the ramparts and setting fire to the fortress. Although it was badly damaged, it was not destroyed. After lengthy battles, negotiations began in 1343 between the opposed sides. A peace treaty from 1345 required the Nelipić family to demolish the new tower at Ključica, causing Konstantin to move his seat from Ključica to Nečven for reasons of security. He left Ključica to his Nelipić relatives from Cetina prior to 1408. At that point, the Croatian-Hungarian King Sigismund, for the sake of reconciliation with the Nelipić family, and “in the name of a new donation“, granted Prince Ivaniš Nelipić the town of Ključ in the Promina dictrict (in districtu Oprominie). The importance of Ključica can be seen in a document from 1450, where it was noted that Venice was prepared to pay 500 ducats, even up to 1000 ducats for its demolition, or to give the ban 200 ducats if the fortress was handed over to the citizens of Šibenik.
At the beginning of the 16th century, the Šibenik and Drniš areas were more and more frequently exposed to attacks by the Ottomans, who thoroughly robbed and looted them. The local inhabitants fled to the fortified cities or to the islands of Šibenik. Around 1522, the Turks occupied almost all the entire hinterland of Šibenik, including Ključica among other places, which remained in their possession up to the Candian War in 1648. Although the fortress, along with some of the other lost territory, was returned to them in negotiations, the Turks abandoned it. It lost its strategic importance, while because of its inaccessible location it remained almost entirely preserved.
Ključica has a rectangular shape. It consists of the fortification and an enclosed suburbium. Within the ramparts are preserved the walls of a multi-story palace, a single story building of unknown purpose, and auxiliary buildings leaning against the northern and northeastern walls. The wall of the suburbium was for the most part preserved, together with the courtyard gates below the western tower, and the remains of fortified gates in the southwestern corner of the courtyard.
Archaeological excavations were undertaken in the southeastern and northern parts of the fortress. Various finds came to light in the investigations: local pottery and fine majolica (13th – 15th cent.), fragments of Gothic architectural elements, fragments of glass, stone projectile balls, and metal objects, predominated by forged iron nails of various dimensions. At the same time as the archaeological excavations, preservations activities were carried out on the architectural remains.