It seems as though, in north/west Europe during the 500s-1000s, shield wall combat predominated in a lot of areas. The Romans had used such formations to batter Germanic and Celtic tribes into submission carrying their scutums and then the beaten tribes began to adopt those Roman tactics.
So my question is, aside from the iron bossed-and-linden/willow board round shield, were there any other shapes of shields that saw serious use during this post-Roman, pre-Norman time? I've seen highly ornamented Celtic shields that give a rough echo of the scutum...were they actually used in the shield wall? Did anyone else try to 'copy' the scutum rather than relying on the round shields?
Unfortunately, because of the materials shields were made out of we cannot really be certain. Indeed, we aren't even certain the 'classic' scutum was a universal design at all used by the legions. That design itself had some disadvantages, and was primarily useful when wielding a short sword, not a spear or the longer swords that became more common in late antiquity. That combined with the greater costs associated with the scutum would have made their usefulness decrease, which might explain the possible shift away to smaller round shields.
The lack of intact finds and real evidence is exactly what I've run into, as well. Although it's not like I've made any comprehensive survey of sources, just a question that kept itching the more I read overall.
It seems as though the round shields were particularly well-suited to the shield wall. They were large enough to cover a man from knee-to-throat when in a crouched fighting position. They were especially sturdy when faced with leather, and even with simple weather-proofing varnish. I've seen pics of reproduction roundshields that are still useful after absorbing 3 or 4 serious strokes from an axe. And their curved shape allowed freedom of movement for a man to wield an axe overhand while still holding the wall position with his shield.
So it's understandable that they were the most common. I've seen a couple people allude to the scutum's space-consuming disadvantages before...I just can't help but feeling that there must have been other designs used because we see so many ornamental shields that look different.
Sorta follow-up question - I've found a fierce debate about whether or not metal stripping was used on the edges of shields. We all know of the classic scutum edging, but were roundshields similarly edged? I feel it's likely that leather facing would've overlapped the edges quite often, with maybe some nails or a few cleats holding it in place. Was metal edging a practice that only noblemen/elite household warriors could have afforded?
Also - the later kite-style shields weren't commonly used by dismounted men...were they?
edit - words are hard sometimes