From prehistoric inhabitants are not left behind either name. The only remains of them testify tools and statues of idols. Archaeological remains speak of indigenous Illyrian tribes that are in fourth century BC conquered the Celts in this area. The Celts are ethnically and culturally mixed with Illyrians and established a settlement Segestica. Illyrian - Celtic tribes succeeded in withstanding Roman pressures to 35 BC when Octavian conquered Segestica with 12 000 troops, after a thirty siege.

In the Roman Empire Siscia changes the status of the military camp, through fortified town to town with full Roman law. Founded in the mid-third century is famous mint, peaking Siscia achieves 297th when he became the center of the province of Pannonia Savia. In this period the city was an important intersection of Roman roads, craft center and the seat of the imperial office for levying taxes.
Christianity, which, despite persecution, Empire spread inexorably caught in the roots Siscia. The first known Bishop of Sisak was Kvirin from 284 until his martyr's death, probably 303rd
The Decline of the Roman Empire, the importance of Sisak and the great migration brought to Sisak Huns, Gale, Avars and Slavs destroyed and largely destroyed the ancient culture.