When Celtic peoples crossed the Pyrenees in the first millennium b.c., they intermarried with the existing Iberian population and built a series of hilltop fort communities or citanias, the finest example of which is at Briteiros (see page 73).
Some Celtic people intermarried with Iberians and built their own communities. 
When the Iberian people crossed the Pyrenees, they exterminated the Celtic people.