I expect the Basque did have a larger area under their control at one time. They probably survived all attacks by withdrawing to the mountains between Spain/France where they live to this day.
You're right. They did control a larger area. In fact, they were known by the Romans as Aquitanians. Linguistic records have proven this beyond a reasonable doubt.
Prehistory and Connections with Other Languages
Scroll down for the information concerning the Aquitanians.