The only evidence come from onomastic data (roughly 200 personal names and about 60 deity names) that have survived indirectly in Latin inscriptions from the Roman imperial period, primarily between the 1st and 3rd centuries AD, with a few possibly dating to the 4th or 5th centuries.

[1] The consensus among scholars is that Aquitanian was a Paleo-European language genetically related to Basque, though there is debate over the exact nature of their relationship.

[3] Aquitanian is attested only in the form of proper names, and we lack enough data to determine their exact meanings.

[5] Drawing on linguistic evidence, Joaquín Gorrochategui concludes that the Aquitanian language was spoken in ancient times (from at least the 1st century BC until the end of the Roman Empire) across a region stretching from Biscay in the west to the Aran Valley in the east, and from the Aquitanian Plain in the north down to the Ebro river in the south.

[6] Most Aquitanian onomastic elements are clearly identifiable from a Basque perspective, matching closely the forms reconstructed by the linguist Koldo Mitxelena for Proto-Basque: