Hey Slubber, here I am at last, just hoping baby won't wake up before I answer your questions.
It was all part of bigger historical re-enactments/re-creations and you would generally camp normally but ultra keen people would get into the authentic camping side of things and have proper historical tents.
I used to do daily life type re-enactments but got sucked into the battle ones despite my natural pacifism, and it has to be said they are brilliant fun.
Sociologically it is all very mockable interesting as you have different groups that do different periods and are always being very superior about the groups that they consider less authentic, so for instance the English Civil War Society are always slagging off the Sealed Knot for an insufficiently purist attitude towards artificial fabrics.
I only ever did things between the 15th and 18th centuries myself but I have met Romans (the Ermine Street Guards are the main ones) and they were all a bit geeky and obsessed with the minute authenticity of their kit and drill, and didn't have very much daily life re-enactment going on, just the military stuff. They were also very strict about only letting people join if they were the right height etc for the actual Roman army, whereas other groups are much more chilled about eg letting women be soldiers.
The scariest re-enactors I ever met were some people that dressed up as Nazis