Gauls
In 58 BC Julius Caesar launched the Gallic Wars and had conquered the whole of Gaul by 51 BC. He noted that the Gauls (Celtae) were one of the three primary peoples in the area, along with the Aquitanians and the Belgae. Caesar's motivation for the invasion seems to have been his need for gold to pay off his debts and for a successful military expedition to boost his political career. The people of Gaul could provide him with both. So much gold was looted from Gaul that after the war the price of gold fell by as much as 20%. While they were militarily just as brave as the Romans, the internal division between the Gallic tribes guaranteed an easy victory for Caesar, and Vercingetorix's attempt to unite the Gauls against Roman invasion came too late. After the annexation of Gaul a mixed Gallo-Roman culture began to emerge.
Netherlands in the Roman era
During the Gallic Wars, the Belgic area south of the Oude Rijn and west of the Rhine was conquered by Roman forces under Julius Caesar in a series of campaigns from 57 BC to 53 BC. He established the principle that this river, which runs through the Netherlands, defined a natural boundary between Gaul and Germania magna. But the Rhine was not a strong border, and he made it clear that there was a part of Belgic Gaul where many of the local tribes were "Germani cisrhenani", or in other cases, of mixed origin. The approximately 450 years of Roman rule that followed would profoundly change the area that would become the Netherlands. Very often this involved large-scale conflict with the "free Germans" over the Rhine.