On the steep cliffs of the gorge between Kozjak and Mosor stands the Klis fortress, with one eye facing the sea and another facing Zagora. It was built on an extraordinary strategic location that allows military and commercial control over the whole Klis valley and the area of Salona and Split. Because of its importance, Klis was often referred to as the key to Dalmatia and the heart of the medieval Croatian kingdom. The findings from the Krčina cave are the first traces of the settlement of the area around Klis fortress. It is ceramic pottery in which different forms are imprinted before the baking from which the name Impresso culture is derived, and it lasts from 6000 to 4500 BC on the Adriatic coast. Today we do not know much about the population of those times, but there is a possibility that there were first traces of agriculture in the Adriatic coast. The first population of this area we can accurately identify are the Dalmatians, one of the Illyrian tribes. They inhabited the area from the river Krka to the Neretva, among others the area along the river Jadro (today’s Solinčica beneath Klis). They raised their forts on natural elevations for easier protection from possible attackers. At the foot of Klis fortress, the remains of such settlement were found, and its role was control of the passage between Kozjak and Mosor. Together with the other nearby forts, the hill below Klis controlled access to Illyrian Salona and the mouth of the river Jadro. This role will take on all of the later buildings at this location. https://www.tvrdavaklis.com/povijest-tvrdave/?lang=en