Archaeological research at Atapuerca indicates the Iberian Peninsula was populated by hominids 1.2 million years ago. In Atapuerca fossils have been found of the earliest known hominins in Europe, Homo antecessor. Modern humans first arrived in Iberia, from the north on foot, about 35,000 years ago. The best known artefacts of these prehistoric human settlements are the famous paintings in the Altamira cave of Cantabria in northern Iberia, which were created from 35,600 to 13,500 BCE by Cro-Magnon. Archaeological and genetic evidence suggests that the Iberian Peninsula acted as one of several major refugia from which northern Europe was repopulated following the end of the last ice age.

The largest groups inhabiting the Iberian Peninsula before the Roman conquest were the Iberians and the Celts. The Iberians inhabited the Mediterranean side of the peninsula, from the northeast to the southeast. The Celts inhabited much of the interior and Atlantic side of the peninsula, from the northwest to the southwest. Basques occupied the western area of the Pyrenees mountain range and adjacent areas, the Phoenician-influenced Tartessians culture flourished in the southwest and the Lusitanians and Vettones occupied areas in the central west. Several cities were founded along the coast by Phoenicians, and trading outposts and colonies were established by Greeks in the East. Eventually, Phoenician-Carthaginians expanded inland towards the meseta; however, due to the bellicose inland tribes, the Carthaginians got settled in the coasts of the Iberian Peninsula.