Ambiorix (fl.54-53 B.C.) was one of the more successful leaders of the resistance to Caesar during the Gallic Wars, winning one of the few clear cut Gallic victories of the war when he destroyed a Roman legion at Aduataca.
Ambiorix was one of two rulers of the Eburones tribe, alongside the elderly Cativolcus. At the end of the campaigning season of 54 B.C. Caesar placed a legion and a half of his troops in winter quarters at Atuatuca, somewhere in Eburones territory, under the command of Q. Titurius Sabinus, with L. Aurunculeius Cotta as his deputy. Ambiorix and Cativolcus met the Romans at the end of their kingdom and pretended to be friendly, but they must already have been planning to revolt.
The revolt of the Eburones was apparently inspired by Indutiomarus of the Treviri. Fifteen days after the Romans went into the winter quarters their foraging parties were attacked while they were gathering wood, and the Eburones attempted to seize the camp. When this attack failed Ambiorix, who was leading the attack, decided to try and convince the Romans to abandon their camp. He told two delegates from the Roman camp that the revolt was general, that Caesar had already left Gail and that a force of Germans was on its way and would attack the camp on the following day. Sabinus fell for this trick, and decided to lead his men out of their fortified camp in an attempt to join up with one of the other legions. Two miles outside the camp the Romans were attacked and their column was almost completely wiped out. Sabinus himself was killed while attempting to negotiate with Ambiorix, apparently in the belief that he was still trustworthy.
This was the most serious defeat suffered by the Romans during the entire Gallic War. Ambiorix headed towards the next Roman camp, that of Q. Cicero, rousing the Aduatuci and Nervii as he travelled. Cicero was less gullible than Sabinus, and refused to leave his camp. Ambiorix and the Nervii besieged Cicero's camp, demonstrating in the process how much they had learnt from the Romans, but Cicero held out until Caesar approached with a relief army. The Gauls abandoned the siege and attempted to stop Caesar, but were defeated and were forced to retreat.
After restoring the situation Caesar returned to his winter quarters. In the following spring he moved against the rebels, leaving Ambiorix and the Eburones for last. Only after every other rebellious tribe had been put down and Caesar had made his second crossing of the Rhine did he turn on Ambiorix.
Ambiorix realised that the Eburones wouldn't be able to defeat the Romans in battle, and so instead of gathering an army he ordered his men to scatter and fend for themselves. A force of Roman cavalry under L. Minucius Basilus came close to capturing Ambiorix early in the campaign, but he escaped into the woods. That was the last time that the Romans saw Ambiorix. He was able to hide out in the Ardennes and avoided capture even when Caesar was using nine full legions to search for him. On a number of occasions the Romans captured prisoners who claimed that Ambiorix was only just ahead of them, but that was as close as they got. Ambiorix is generally assumed to have escaped across the Rhine into the lands of his German allies, but he was clearly still seen as a threat in 51 B.C., when having defeated the last rebels in the north-east of Gaul Caesar devastated Ambiorix's former territory in an attempt to make sure that he wouldn't be welcomed back the moment Caesar left for Italy.