Carcassonne became strategically identified when Romans fortified the hilltop around 100 BC and eventually made the colonia of Julia Carsaco, later Carcasum (by the process of swapping consonants known as metathesis). The main part of the lower courses of the northern ramparts dates from Gallo-Roman times. In 462 the Romans officially ceded Septimania to the Visigothic king Theodoric II who had held Carcassonne since 453; he built more fortifications at Carcassonne, which was a frontier post on the northern marches: traces of them still stand. Theodoric is thought to have begun the predecessor of the basilica that is now dedicated to Saint Nazaire. In 508 the Visigoths successfully foiled attacks by the Frankish king Clovis. Saracens from Barcelona took Carcassonne in 725, but King Pepin the Short (Pépin le Bref) drove them away in 759-60; though he took most of the south of France, he was unable to penetrate the impregnable fortress of Carcassonne.