The first written reference to the name Cantabria emerges around 195 BC, in which the historian Cato the Elder speaks in his book Origines about the source of the Ebro River in the country of the Cantabri:

…The Ebro River starts in the land of the Cantabri, large and beautiful, with abundant fish…

— Cato the Elder, Origines: VII

There are about 150 references to Cantabria or the Cantabri in surviving Greek and Latin texts. The Cantabri were used as mercenaries in various conflicts, both within the Iberian Peninsula and elsewhere. It is certain that they participated the Second Punic War, from references by Silius Italicus and Horace. When C. Hostilius Mancinus was besieging Numantia, he withdrew upon learning that Cantabri and Vaccaei were present among his auxiliaries. The Cantabrian Wars began in 29 BC. They were defeated by Agrippa with great slaughter in 19 BC, but they revolted again under Tiberius and were never entirely subdued.

In older geographers, the term Cantabria referred to an expansive country bounded by the Cantabrian Sea (the Bay of Biscay), the western side of the Sella valley in Asturias, the hillfort of Peña Amaya in Burgos, and along the Aguera River almost as far as Castro Urdiales. It thus included areas of Asturias, Santander, Biscay, and Guipuzcoa. Following the Roman conquest of Spain, however, it was restricted to the area of Santander and eastern Asturias, forming a part of Hispania Tarraconensis (“Tarragonan Spain”). The principal tribes of the area were the Pleutauri, the Varduli, the Autrigones, the Tuisi, and the Conisci or Concaui, who were known for feeding on their horses’ blood. The area was well settled, with the largest city being Juliobriga, and the local mountains exploited for lead mines.