Quote Originally Posted by blitzkrieg80
you might be interested to know that I am suggesting a name-change of Carrodunum to Karrodunon similar to what you suggested, since there is no reason such a far-away place would be Latinized during the EB start... so you were right on that

how could it be Castoi? isn't there a st/tt>ss rule? i am curious more than anything because i dont really understand how this rule applies to some things but not on others
What there is, in Gaulish specifically, is a change of st to "Tau Gallica" (similar to an eð but with the stroke all the way across) pronounced /ts/ or /ss/ hence the goddess Sirona (whose name derives from earlier ster-) sometimes appears as Ðirona. Since we've got words like cast, cystal and stwc in Welsh, it appears this change didn't happen in Brythonic, so if the meaning is curly-haired/complicated/handsome then it would have been *Castoi. Caesar used Gauls as interpreters in Britain, so they may pronounced it cass- or cats-.