And it’s worth understanding that as auxiliaries (non-citizen soldiers) were assigned to provinces other than the ones in which they were recruited…a Black person who enlisted in North Africa could well be sent to Britain, spend 25 years there, marry a local girl and…
Let’s just say that a LOT of white Europeans have genetic markers which indicate African ancestry during this time…between retired soldiers getting married, current soldiers visiting their sweethearts and/or brothels, traders from Africa…there would have been lot of mixed race kids running around, especially in towns close to forts.