Appian(us) (c.AD 95 – c. 165) was born in Alexandria but went to Rome in c.120 to practice law. We are not entirely sure about what sources he used for his histories.
The following is an Appian. The Foreign Wars, trans. Horace White. New York: MacMillan Company, 1899.
§ 1. The Pyrenees mountains extend from the Tyrrhenian sea to the Northern ocean. The eastern part is inhabited by Celts, otherwise called Galatians, and more lately Gauls. From this part westward, beginning at the Tyrrhenian sea and making a circuit by way of the Pillars of Hercules to the Northern ocean, the Iberians and Celtiberians dwell. Thus the whole of Iberia is sea-girt, except the part embraced by the Pyrenees, the largest and perhaps the most precipitous mountains in Europe. In coasting they follow the Tyrrhenian sea as far as the Pillars of Hercules. They do not traverse the Western and Northern ocean, except in crossing over to Britain, and this they accomplish by availing themselves of the tide, as it is only half a day’s journey. For the rest, neither the Romans nor any of the subject peoples navigate that ocean. The size of Iberia (now called “Hispania” by some) is almost incredible for a single country. Its breadth is reckoned at ten thousand stades, and its length is equal to its breadth. Many nations of various names inhabit it, and many navigable rivers flow through it.
What nations occupied it first, and who came after them, it is not very important for me to inquire, in writing strictly Roman history. However, I think that the Celts, passing over the Pyrenees at some former time, mingled with the natives, and that the name “Celtiberia” originated in that way.