Because of this incident, the Aedui tribe were allies of Caesar and when the Aedui felt threatened by the Arverni, they began to trade grain for Romans soldiers to build up their armies.
There had always been a lot of unrest among the Gauls as Caesar's army began to have more control over the country and as the Roman philosophies infiltrated the tribes. There were many revolts and small scale rebellions which the Roman army dealt with easily. However the Romans knew that if ever the Gallic tribes formed an alliance, it would not be so easy.
Rebellion
One tribal prince, Celtius of the Arverni, tried to do just that and to make himself King of all free Gaul. This is supposedly against the Gallic beliefs and it punishable by death, however when he was found murdered, evidence pointed that Roman weapons had been used when, if he was due for death, the druids would have done it. Celtius' son, Vercingetorix was furious and blamed the Romans. He also realised that if they wanted to remain free, they would have to join all the together. The Carnutes were the first to respond because on their land was the sacred grove which was the holiest place in the country. The head druid was elected there and it was where the druids met. The Carnutes asked the other tribes to bring their military standards together which was a very solemn oath, and to swear not to desert them when the war started.
The result was that on an appointed day, the Carnutes, lead by Cotuatus and Conconnetodumnus, entered Cenabum and killed all the roman citizens who had settled there and plundered their property. When the news spread through the country, reaching Arverni, Vercingetorix called all his descendants together and told them of his planned rebellion. Once word spread more people joined his army. He first went to get support from his fellow Arvernians and then from other tribes such as the Senones, the Parisii, the Pictones, the Cadurci, the Turoni and all other tribes along the Atlantic coast. Vercingetorix moved his forces towards the Bituriges who were allies of the Aedui but a fairly strong tribe in their own right. When the realised he was coming, they sent word to the Aedui for help and the Aedui sent out Roman cavalry and infantry. However, once the troops reached the R. Loire separating the two territories, they were too scared to cross it and left after three days. With this, the Bituriges allied themselves with the Arverni
The Fall of Cenabum
Now that he had control over the lands of the Bituriges, Vercingetorix started to lead his army to the Boii oppidum of Gorgobina whom Caesar had settled under the protection of the Aedui after he had defeated them in battle. Caesar sent word that he was going to come and help them. On the way he stopped his troops at Vellaundunum, oppidum of the Senones, and set up siege.