In the twelfth century B.C., Phoenicians arrived on the west coast of the Iberian Peninsula in search of metals and founded trading posts at Cádiz, Málaga, and Seville. They traded with the peoples of the interior, taking out silver, copper, and tin and bringing in eastern trade goods. Between the eighth century and sixth century B.C., successive waves of Celtic peoples from central Europe invaded the western part of the peninsula, where the topography and climate were well suited to their herding-farming way of life. They settled there in large numbers and blended in with the indigenous Iberos, giving rise to a new people known as Celtiberians. Their settlements were hilltop forts called castros, of which there are many vestiges in northern Portugal.

Later, during the seventh century B.C., Greeks arrived and founded several colonies, including Sargunto on the Mediterranean coast and Alcácer do Sal on the Atlantic coast. During the fifth century B.C., the Carthaginians replaced the Phoenicians and closed the Straits of Gibraltar to the Greeks. The Carthaginians undertook the conquest of the peninsula but were only able to permanently occupy the territory in the south originally controlled by their Phoenician and Greek predecessors. The Carthaginian occupation lasted until the defeat of Carthage by the Romans in the third century B.C.

The Romans made the former Carthaginian territory into a new province of their expanding empire and conquered and occupied the entire peninsula. This invasion was resisted by the indigenous peoples, the stiffest resistance coming from the Lusitanians who lived in the western part of the peninsula. The Lusitanians were led by warrior chieftains, the most powerful of whom was Viriato. Viriato held up the Roman invasion for several decades until he was murdered in his bed by three of his own people who had been bribed by the Romans. His death brought the Lusitanian resistance to an end, and Rome relatively quickly conquered and occupied the entire peninsula. The Portuguese have claimed Viriato as the country's first great national hero.

Data as of January 1993