The siege of Gorgobina (early 52 B.C.) saw Vercingetorix make an unsuccessful attack on a town that was under the protection of Julius Caesar. The Gauls were forced to lift the siege when Caesar approached from the north with his main army and besieged Novidunum, but the attack had forced the Romans to leave their winter quarters much earlier than they would have liked.
The location of Gorgobina is unknown. It was settled in 58 B.C. by the Boii, a tribe that had accompanied the Helvetii on their migration. Caesar's allies, the Aedui, had recently suffered a defeat at the hands of the Sequani and their German allies, and after the final defeat of the Helvetii they asked Caesar to allow the Boii to settle in Aedui territory as their allies. The town was thus probably somewhere between the Saone and the upper Loire.
After learning of the outbreak of the great Gallic revolt Caesar left the Italian part of his province, returned to Gaul, and at the head of a small army crossed the Cevennnes Mountains into the territory of the Arverni. Vercingetorix was forced to move south from the lands of the Bituriges to defend his homeland. Once Caesar was sure the Vercingetorix was on his way he slipped away to the north, and was soon able to rejoin his legions in their winter quarters.
Once he discovered that Caesar had slipped past him Vercingetorix moved back into the lands of the Bituriges and then turned east to besiege Gorgobina. Caesar admitted in his commentaries that this move caused him 'great perplexity'. The entire campaign was taking place in later winter, and food was thus in short supply. Caesar was aware that if he led his men out of their winter quarters then they might run out of supplies. The alternative was worse. If the Romans remained in their winter camps and allowed Vercingetorix to take Gorgobina, then Rome's remaining allies in Gaul would no long expect protection from Caesar, and many more tribes would probably join the uprising.
Caesar decided that he would have to lift the siege of Gorgobina. Leaving two legions and his baggage at Agendicum (modern Sens, fifty miles to the south east of Paris) he led the rest of his army towards the Boii, sending messages ahead to encourage them to keep fighting.
Caesar clearly decided that the best way to raise the siege of Gorgobina was to attack a series of Gallic towns and force Vercingetorix to move against him. On the second day of his march he reached Vellaunodunum (possibly at Montargis or Château-Landon), which fell after three days. He then moved on to Genabum (or Cenabum), now modern Orleans on the Loire, which also fell after a short siege. From there the Romans moved to attack Novidunum (probably Neung sur Beuvron, about thirty miles to the south of Orleans).
Just as Caesar had hoped the attack on Novidunum forced Vercingetorix to abandon the siege of Gorgobina. The two side's cavalry clashed close to Novidunum, but the town quickly fell to the Romans and Caesar moved on to attack Avaricum.