Long story short, I'm a history dabbler, post Roman Britain being of particular interest, probably more knowledgeable than most but nowhere near the standard that I see here. I've gotten hooked on a show (not Vikings) and the history is much more solid than I'm used to, not good enough to believe hook line and sinker but good enough to suspect a very solid historical consultant.

One thing of note is that all sides (usually Saxon vs. Danes) are using shield walls, this is good, I understand they were common. I like the depiction of combat as primarily a shoving match, assisted by sharp and pointy things to break the wall.

I'm confused if there is a historical basis for the formations they are using.

I've seen the Saxon shield wall as depicted on the Bayeux Tapestry, close rank, shields locked but only one level of shields. These forces are depicted with multiple levels of shields (low, chest, overhead) almost like a variant on the Roman Testudo, which to my understanding wasn't a fighting formation, just missile protection while moving.

I know sources are sketchy, but is there source material out there actually describing anything resembling that?