Euskara is a language isolate. It has no demonstrated relationship to any other living language, and attempts to attach it to Iberian, to Caucasian families or to anything else have not been accepted. That fact has carried a heavy load of speculation about the antiquity of the Basques, and Roger Collins's history is a useful corrective: a language without relatives tells you about the language, not about an unbroken population.
What the record shows is a people occupying the western Pyrenees and the coast at the edge of successive states rather than outside them. Rome had a presence there, the Visigoths and the Franks both campaigned in the region, and the ambush at Roncesvalles in 778 that destroyed Charlemagne's rearguard, and became the Song of Roland, was in the earliest accounts the work of Basques rather than of Muslims.
The Kingdom of Navarre and the provincial fueros gave the Basque territories a distinct legal standing that survived into the nineteenth century and was progressively removed after the Carlist wars. Modern Basque nationalism dates from that removal, and its founder, Sabino Arana, made Catholicism part of his definition of the nation. Euskara, driven out of public use under the Franco regime, is now co-official in the Basque Autonomous Community and in part of Navarre, and is taught through the ikastola school network.