Late Roman belt

[Medicus matt]

I'm not sure why you think that. .

Because I've worn mailshirts for up to 8 hours a day on a regular basis for the last 20 years.
For most of that I followed the norm and wore a tight waistbelt over the mail as well as a sword belt. I stopped doing that a couple of years ago when somebody pointed out that it was very, very rare to see depictions of men in mail in the late roman/early medieval period (the fact that every time this debate arises it's just one depiction in one mosaic that gets held up as evidence rather proves that point I think). Having looked into it myself, I concluded that wearing a belt over mail seemed to be the exception rather than the norm, so decided to give it a try.

Not wearing a belt makes no noticeable difference to the weight on the shoulders because, unlike a backpack, mail has no supporting framework so the belt provides no weight carrying suppport except to the very small amount hanging below the belt. On a full length hauberk which comes down to below the knees, it would make a noticable difference, but not on a mid thigh length shirt.

What I have found is that not wearing a belt allows the mail to move more freely, which seems to make movement overall much easier, especially when moving the arms in combat.
I would imagine that it would also make it more effective as armour as it hangs over the body and can move under impact, rahter than being hold more tightly in place as it is when secured by a belt. That's speculation, and difficult to test but makes sense, to me anyway.

As for the point about wanting to take your knife into battle.... why? I've yet to see a late roman knife that'd was designed to be a side arm rather than a general purpose knife. Certainly nothing like the offensive big knives of the Germanic/Scandinavian cultures. I'll leave it back in the camp/billet, along with my cash and other portable wealth.