Quote:Does archaeology reveal the dimensions of the 23 forts Caesar initially built to keep Vercingetorix's forces within Alesia?
Sadly, not. Napoleon III's collaborators drew up a sequence of 23 forts dotted around the siegeworks, but only five were based on traces on the ground; eighteen were entirely imaginary. Worse still, two of the five were later established as non-Roman, leaving only Napoleon's #11, 15 and 18 as
probably Roman.
I should say that there were camps, too. Napoleon drew up a sequence of 8. Only A, B, and C (with an outside possibility of G) are now thought to exist, giving us a series of six camps/forts around the south and east of Alesia.
More interesting is the "new" feature (discovered in the 1990s) on the western sector of the siegeworks, where there appears to be a fort marked out between the inner and outer siegelines. It was designated "4 bis" because it lies near Napoleon's imaginary fort #4.
This is the most promising candidate for one of Caesar's
castella. If you're interested, it's roughly 120m square. Nothing was found inside.
For light reading, you could try
Ancient Warfare magazine, Vol. 2, Issue 4 (2008).
For heavy reading, there's M. Reddé, S. von Schnurbein, et al., "Fouilles et recherches nouvelles sur les travaux de César devant Alésia (1991-1994)", in
Bericht der Römisch-Germanischen Kommission 76 (1995), pp. 73-157.