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 a 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.

The spread of the Romans lead to contacts and conflicts between the local Illyrian population and the conqueror from Lazio. After long-lasting wars, the Illyrian uprisings were finally overwhelmed by the crushing of Baton’s uprising in the 9th century AD. In the late Roman period, the Roman fort of Kleis was established as a protection of Salona, the ancient metropolis of Roman Dalmatia.

The fall of the Roman Empire brought the Salona area and the Klis fortress under the rule of the Byzantine Empire in whose hands they will remain until the arrival of new conquerors from the northeast. The guard above Salona was finally defeated in 614 when the Avar-Slavic horde passed through the fort, supposedly by fraud. The horde will continue and destroy Salona, whose population will seek shelter behind the walls of Diocletian’s Palace, the nucleus of today’s Split.

For the next 200 years it is hard to say what was happening at the foot of Klis, primarily because of large migrations and falling literacy. In this period Croats came to Dalmatia, and probably saw the Adriatic Sea for the first time from the Klis fortress with which to date they have an unbreakable connection. Duke Trpimir charter in 852 mentions that Klis is one of the ruler’s fiefs and in the next seven centuries it will change its ownership a number of times. Klis also played a big role during the Mongolian pillages when the horde saw the Klis Fortress and turned away.

Klis’s greatest significance for Croatian history dates back to the 15th century when it found itself at the crossroads of the three empires – the Ottoman Empire, the Venetian Republic and the Habsburg Monarchy. Klis was the home of the Uskoks, military units that got their name because they jumped into („uskočiti“ in Croatian) the enemy territory, pillaged it and returned to their base. The leader of the Klis Uskoks was Petar Kružić, who defended the fortress with his men for more than twenty years against powerful Ottoman army. Nevertheless, with very poor help from the Habsburg ruler Klis could not resist forever, and in 1537 it fell into Turkish hands.

Fot the next 111 years Klis will be in the hands of Ottomans. During that period there were several attempts by the Venetians or Uskoks to retake the fortress times, and in 1596. they succeeded in their plan. Approximately hundred Croats led by the Split nobles conquered the fortress by suprise, after which their fellow countrymen came to aid. However, the same year there was a counterattack of the Ottomans with a significantly greater army, which ultimately made the fortress defenders desert their positions and leave the city.

Fortress Klis had its last major role in the military sense during the War of Candia between the Venetian Republic and the Ottoman Empire. Many bloody battles for the fortress were fought, which in the end fell into the hands of the Venetian army in which many Croatians were conscripted. From that point on, Klis will no longer see larger military action beneath its walls – it remains in Venetian hands until 1797 when it comes under the French rule. By the fall of the First French Empire fortress became part of the Habsburg Monarchy, and with its abolishment it shared the fate of Croatian territories until 1990, when the flag of Republic of Croatia was flown over it.