Historic references to the city go back to the 4th century and to Roman times, although Celtic and Proto-Celtic remnants of ancient Citadels were found in the heart of where Porto now lies. In the Roman period the city developed its importance as a commercial port, primarily in the trade between Olissipona (Lisbon) and Bracara Augusta (nowadays Braga), but would fall under the Moorish Muslin invasion of the Iberian Peninsula in 711. In 868, Vímara Peres, a Christian warlord from Gallaecia and a vassal of the King of Asturias, Léon and Galicia, Alfonso III, was sent to reconquer and secure from the Moors the area from the Minho River to the Douro River, including the city of Portus Cale, later Porto and Gaia, from were the name and political entity of Portugal emerged. In 868 Count Vímara Peres established the First County of Portugal (Portuguese: Condado de Portucale), after the reconquest of the region north of the Douro river.