As a point of discussion; Alesia is, on the face of it, a simple military blunder by Vercingetorix. I see this military blunder as being precipitated by the political instability of the Gallic uprising that he lead. Vercingetorix, I would argue, based his decision to remain within Alesia on the basis of the political situation he faced.

In order to even begin the rebellion he had to face down factions of the nobility within his own tribe. When the Aedui joined the uprising they attempted to have the command of it transferred to them - away from Vercingetorix. We see his internal enemies raise their heads again following the siege of Avaricum. There he was accused of 'treason' for having left the army without a commander. He managed to overcome these accusations by rightly showing how the army were left in a position unfavourable to attack by their enemies (as Caesar attests).

So, here he is at Alesia. The best military decision that he could make would have been to have escaped with his cavalry in order to co-ordinate the relief of Alesia. That way Caesar would be turned from the besieger to the besieged - with little hope of relief himself. So, Vercingetorix made a simple tactical blunder? I think that he knew that leaving Alesia un-commanded would have been the end of him, so he was left to trust to the military co-ordination ofothers....not all of whom were (perhaps) quite as...... committed as he was to ridding Gaul of the Romans.

Had Vercingetorix had the political power to do so he would almost certainly have escaped Alesia. He could not because the Gauls were divided by internal politicking.