 Despite the Illyrians being subject to a strong process of acculturation, they continued to speak their native language, worship their own gods and traditions, and follow their own social-political tribal organization which was adapted to Roman administration and political structure only in some necessities.The collapse of the Western Roman Empire, with the beginning of the Migration Period, left the region subject to Gothic rulers Odoacer and Theodoric the Great.They ruled Dalmatia from 480 to 535 AD, when it was restored to the Eastern (Byzantine) Empire by Justinian I.