In the summer of 57 BCE, the Roman general Julius Caesar invaded the country of the rivers Scheldt and Meuse. Proceeding along an ancient road, first defeated the Nervians in the Battle of the Sabis in Flanders and continued to the east, where he forced the Aduatuci of eastern Belgium into submission. According to his own statistics, almost 60,000 Nervians were killed and 53,000 Atuatuci were sold as slaves. The first number is probably exaggerated, but human misery must have been great.
This show of force marked the beginning of the Roman occupation of the Meuse valley, which was to last for more than four and a half centuries. At first, the Romans were content to dissolve the old political ties. For example, strong tribes were forced to free their client tribes (i.e., dependent tribes). The only truly repressive measure must have been the seizing of hostages, a common instrument to keep subjects subjected.
Among those freed in the autumn of 57, were the Eburones, a tribe living between the rivers Meuse and Rhine. They may have been grateful at first, but this changed in the winter of 55/54, when the Romans for the first time built camped in northern France and Belgium, and the weight of the occupation became heavier. However, the Romans did not notice or ignored their discontent.
Instead, they spent the summer in Britain, where Caesar defeated Casivellaunus, the war leader of the united British tribes. In their absence, the Belgian tribes -even more discontent because of a bad harvest- prepared a rebellion. (Evidence for their cooperation is the so-called "treasure of Ambiorix", which consists of coins of several tribes.) When the legions returned and spread out to their winter quarters, the rebels were ready to strike. They had timed their attack excellently: in the winter, when Caesar had gone south to visit his province Gallia Cisalpina (northern Italy). Their first target was well-chosen too: the recently recruited Fourteenth Legion with five cohorts, stationed among the Eburones.
The leader of the revolt was Indutiomarus, the leader of the Treverians, a tribe that lived in the valley of the Moselle. It is not clear what gave him the right to order the Eburones to attack the Romans, but it is probable that the Eburones had become a Treverian client tribe. However this may be, it is clear that the Treverians used the Eburones as a lightning rod: only when the northern tribe was successful, they would unmask themselves. Otherwise, they would keep themselves out of harm's way.
The rebellion is described by the Greek historian Cassius Dio (164-c.235) in this link.