Vercingetorix has retreated to the safety of the territory around Gergovia, from where he has masterminded a coup inside the tribes loyal to Caesar. The sedition eventually fails but Caesar loses precious time and resources which could have been devoted to the siege of Gergovia.

 

A Hill Too Far

Gergovia is located on a hill and Vercingetorix has posted his troops on all the summits around it. Caesar has built his main camp on a hill nearby with all the care the Roman war machine affords him, and a smaller one closer. Soon, he notices that a last hill, closer to the city, would offer a precious advantage to the Romans because...

if they should lose the other, they would be almost surrounded, and cut off from all egress and foraging

So, Caesar sets a night attack with the following disposition. While his troops will have to conquer the smaller hill…

He sends one legion to the same hill, and after it had marched a little, stations it in the lower ground, and congeals it in the woods.

...the tribe of the Aedui will distract Vercingetorix by attacking his camp:

To these he adds a few cavalry, with instructions to range more widely to make a show. He orders them all to seek the same quarter by a long circuit; these proceedings were seen at a distance from the town, as Gergovia commanded a view of the camp, nor could the Gauls ascertain at so great a distance, what certainty there was in the maneuver. 

And hopefully, they will have in the morning the possession of a key position to obtain the surrender of Gergovia.

A clear cut map of the forces and their movements [Source]

Night attack

Vercingetorix does notice the maneuver but does not yet understand that Caesar’s goal is to conquer the hill. He actually was aware of the strategic importance of the hill, since this one was defended:

But almost in the middle of the hill, the Gauls had previously built a wall six feet high, made of large stones, and extending in length as far as the nature of the ground permitted, as a barrier to retard the advance of our men

But without sufficient men, and confused by the maneuver of Caesar, these walls were useless against a full scale attack: 

The soldiers, on the signal being given, quickly advance to this fortification, and passing over it, make themselves masters of the separate camps. And so great was their activity in taking the camps, that Teutomarus, the king of the Nitiobriges, being suddenly surprised in his tent, as he had gone to rest at noon, with difficulty escaped from the hands of the plunderers, with the upper part of his person naked, and his horse wounded. 

Vercingetorix busy repulsing the decoy attack, and the smaller hill in the hands of his men, Caesar thought that the victory was his. But for once, his masterplan was ruined by his own men:

being animated by the prospect of speedy victory, and the flight of the enemy, and the favorable battles of former periods, they thought nothing so difficult that their bravery could not accomplish it; nor did they put an end to the pursuit, until they drew nigh to the wall of the town and the gates

Everything falls apart

Caesar’s men, probably encouraged by the memory of the siege of Avaricum, did not hear the order to stop and regroup and kept going in direction of Gergovia:

being animated by the prospect of speedy victory, and the flight of the enemy, and the favorable battles of former periods, they thought nothing so difficult that their bravery could not accomplish it; nor did they put an end to the pursuit, until they drew nigh to the wall of the town and the gates

The attack drew panic inside Gergovia. Everyone inside the town thought that the town was going to fall in the hands of the Romans and would suffer the same fate as Avaricum, but little by little they realized that the Romans soldiers were much less numerous than thought and feared. So, the Gauls regrouped and started to fight back, with success:

Neither in position nor in numbers was the contest an equal one to the Romans; at the same time, being exhausted by running and the long continuation of the fight, they could not easily withstand fresh and vigorous troops.  

Even worst: the Aedui, once their diversion job done, had retreated and met the Romans troops. In the confusion, Romans and Aedui started fighting each other:

the Aedui suddenly appeared on our exposed flank, as Caesar had sent them by another ascent on the right, for the sake of creating a diversion. These, from the similarity of their arms, greatly terrified our men; and although they were discovered to have their right shoulders bare, which was usually the sign of those reduced to peace, yet the soldiers suspected that this very thing was done by the enemy to deceive them

Eventually, the Romans manage to reach safely back the plain:

The legions, as soon as they reached the plain, halted and faced the enemy. Vercingetorix led back his men from the part of the hill within the fortifications. On that day little less than seven hundred of the soldiers were missing. 

Retreat

The next day, Caesar admonished his soldiers for their greed and for not listening to his orders in the strictest terms:

he censured their licentiousness and arrogance, because they thought that they knew more than their general concerning victory, and the issue of actions: and that he required in his soldiers forbearance and self‐command, not less than valor and magnanimity.

In spite of the way Caesar paints the battle and the ensuing retreat, Gergovia is a clear defeat for Caesar. Vercingetorix is secure in Gergovia and Caesar is now more than ever worried about his alliance with the Aedui, because the town of Noviodunum has fallen in the hands of rebels:

having put to the sword the garrison of Noviodunum, and those who had assembled there for the purpose of trading or were on their march, they divided the money and horses among themselves; they took care that the hostages of the [different] states should be brought to Bibracte, to the chief magistrate; they burned the town to prevent its being of any service to the Romans, as they were of opinion that they could not hold it

Caesar has therefore no other choice than to abandon the siege of Gergovia and to move north in order to consolidate the alliance of tribes still loyal:

he moved his camp in the direction of the Aedui. The enemy not even then pursuing us, on the third day he repaired the bridge over the river Allier, and led over his whole army.  

                                              

                              The monument elevated to the memory of the battle, in Central France [Source]

In spite of the understated way Caesar paints his defeat, Gergovia is truly a victory for the Gauls and Vercingetorix. The Romans, usually so great at conquering cities, have been checked and repulsed, and their prestige has been shattered. And during all this time, the great revolt has had time to find new support… Is it the start of the end for Roman Gaul?

 

To be continued...

SOURCES 

http://www.historyofwar.org/articles/wars_gallic.html

https://prezi.com/yikozvla9o9a/gallic-wars-timeline/http://www.ancient.eu/vercingetorix/http://www.livius.org/articles/person/caesar/caesar-04/

http://stcharlesprep.org/01_parents/oneil_j/Useful%20Links/AP%20Latin%20Assignments/HW/The%20Gallic%20Wars.pdf