Celtic settlement of Southeast Europe

Gallic groups, originating from the various La Tène chiefdoms, began a southeastern movement into the Balkans from the 4th century BC. Although Gallic settlements were concentrated in the western half of the Carpathian basin, there were notable incursions and settlements within the Balkans. From their new bases in northern Illyria and Pannonia, the Gallic invasions climaxed in the early 3rd century BC, with the invasion of Greece.

Source: Wikipedia — Celtic settlement of Southeast Europe (CC BY-SA 4.0)