Cultural and linguistic similarities were also formed as a result of contacts between the non-Indo-European Iberians and the Indo-European Celts in northern Spain. Presumably, this was a kind of symbiosis or just a different neighbourhood with a certain cultural influence on each other, not always peaceful interactions.
The Celts invaded over the Pyrenees between 800 and 500 BC and at times overran large parts of the peninsula, settling mainly in the north and centre of the peninsula. Their identity on the Pyrenean peninsula was profoundly influenced by Iberian traditions, so that one speaks of a Celtic-Iberian fusion culture and finally of the ethnic group of the Celtiberians. It is unclear whether and to what extent the Celtiberian tribes actually emerged from a fusion between Celts and Iberians or essentially represent one of the two groups.
The Celtiberians never formed a political unit; it is significant that they did not have their own collective name. They fell into different tribes. These, too, did not form political umbrella organisations, but fell apart into independent families, clans and communities.