Neolithic era to the Roman Empire

During the Neolithic the region was inhabited by Iberian related peoples, who also lived in other regions of Atlantic Europe at the time. They built religious monuments called megaliths. Dolmens and Menhirs still survive in the countryside around the city.

The Indo-European Celts invaded after the first millennium BC and intermarried with the Pre-Indo-European population, giving a rise to Celtic-speaking local tribes such as the Cempsi.

Archeological findings show that a Phoenician influence existed in the place that, since 1200 B.C., leading some historians to the theory that a Phoenician trading post occupied the site of the centre of the present city, in the southern slope of the Castle hill. The magnificent harbour provided by the estuary of the river Tagus made it the ideal spot for a settlement to provide foodstuffs to Phoenician ships travelling to the tin islands (modern Isles of Scilly) and Cornwall.