History Memes

None that are contemporary. Some later Roman historians used other sources (which are not available to us, unfortunately).

More broadly, though, the core issue is that at Alesia, the big risk was Vercingetorix escaping with his force, rather than the Roman force being crushed inside the siege lines. The final major assault by the Gallic forces was focused on a single camp which was perceived as a weak spot in the mutually-supporting-and-fortified positions - if the assault had succeeded, the result would not have been the destruction of the Roman force (which would remain, even damaged, in a largely defensible position that could not be starved out by the logistically-strained Gallic army outside of the fortifications), but the rescue of Vercingetorix and the further emboldening of the uprising.

While that could have led to Vercingetorix eventually winning the war, Caesar's fortifications during the siege ensured that losing would damage the Romans and deny them victory (and perhaps more worrying to Caesar, damage his political standing at Rome), but winning would crush the Gauls. Asymmetric risks.