How far did Basque-speaking areas extend during the early Common Era?

At the beginning of the Common Era, dialects of the Euskarian (Basque) stock were spoken in areas both north and south of the Pyrenees mountains. The eastern extent of these dialects reached as far as the Aran Valley in northeastern Spain.1

It is believed that the Basque language held a firm foothold in the region that became known as Vasconia. During this period, the language likely experienced a significant expansion toward the southwest, extending into the Rioja Alta region of Old Castile and reaching areas near Burgos. While the disruption of Roman administration in these regions may have helped preserve Basque dialects from being entirely replaced by Latin, other eastern dialects were eventually separated from the main Basque-speaking area by speakers of Romance languages.1