The Dordogne has evidence of Mousterian industry from 40,000 BC and of Cro-Magnon man of the Upper Paleolithic period. With the end of the Ice Age, agricultural settlement appeared around 7000 BC. By the beginning of the 8th century BC, Celtic tribes from Central Europe were inhabiting the Rhône valley of Gaul (now France) while the Greeks were building cities such as Massalia (Marseille) along the Mediterranean coast. The Romans crossed the Alps into southern France in 121 BC and Gaul was conquered by Julius Caesar in 52 BC. The country benefited from protected trade routes and from Roman infrastructure, speech and government. Roman rule was consolidated by the reign of Augustus at the end of the 1st century AD. But the Empire was threatened by Germanic (‘barbarian’) incursions from the north and east. Many of these tribes were assimilated as foederati (treaty nations) into the Gallo-Roman Empire but they assumed authority in their domains as Roman government receded in the 4th and 5th centuries. After the repulse of Attila and his Huns in 451, the Salian Franks emerged as the strongest of the Germanic tribes—their leader, Merovius, was the progenitor of the Merovingian dynasty that ruled France until the beginning of the 8th century.