Its unique position makes the town of Omiš extraordinary. It has sprung on the very mouth of the Cetina River as a pirate fortress, and its beginnings had been mentioned even in the ancient Greek and Roman times.
The Cetina River has had its influence on the administrative and political significance of the city of Omiš, as well as its historical development.
Passing along the left side of the Dinara-Mountain-of-Omiš massif and border parts of Poljica, in ancient times the mouth of the Cetina River was approximately six kilometres upstream by the waterfalls in Radmanove Mlinice. The river erosion consequently formed sandy terraces, and in today’s mouth it formed the Punta peninsula where today’s Omiš has spread.
In the late Bronze and Iron Age, settlements of a hill-fort type were built in the vicinity of today’s Omiš as well as their sentry posts in strategically important positions (Očur, Gradac, Starigrad, Careva gomila and Glavica). These objects allowed monitoring maritime routes towards the island of Brač and the mouth of the Cetina River.

The Omiš of today is a peaceful town with approximately 7 000 inhabitants at the mouth of the Cetina River and approximately 17 000 inhabitants in the whole administrative territory of the town, which comprises Upper, Middle and a part of Lower Poljica as well as the eastern coastal area from Nemira to Dubci.
It is difficult to comprehend that in the Middle Age it was a dangerous pirate stronghold, feared by all theships in the Adriatic Sea. At the time of their heaviest raids the pirates of Omiš were led by the princes of the family of Kačić. The pirates of Omiš achieved their domination over the Adriatic Sea with bravery and specially constructed ships called sagitae (arrows).
For a while Omiš belonged to the Principality of Neretva, and since King Petar Krešimir IV, 1058 – 1074, to the old Croatian state. Since 1444 Omiš belonged to the Republic of Venice. In 1601 it had 1300 inhabitants, and under Venetians it became an unconquerable fortress in the fight against Ottomans. In 1797 it came under the administration of Austria, in 1806 under the administration of Napoleon and from 1813 to 1918 again under the administration of Austria. At that time it was an administrative and transportation centre of the Dalmatian hinterland (Dalmatinska Zagora).