A tribe known as the Illyroi are known to have occupied a small and well-defined part of the south Adriatic coast, around Skadar Lake astride the modern frontier between Albania and Montenegro.

The Illyrian invasion is estimated to have occurred around the 13th century BC. According to this theory, the Illyrian invasion most likely caused the Phrygian migration from Thrace into central Asia Minor.

During the 5th century BC, a well-developed Illyrian population center existed as far north as the upper Sava River valley in what is now Slovenia. Illyrian friezes discovered near the present-day Slovenian city of Ljubljana depict ritual sacrifices, feasts, battles, sporting events, and other activities.

At various times, groups of Illyrians migrated over land and sea into Italy.

Central to their beliefs was the concept that everything was "born" by Mother Earth, who was represented by the Goddess "Genusus."