I’m Netflix’s the last kingdom (Spoiler) it shows the main hero and Another Viking Faction fighting Shield Wall to shield wall, Did is this accurate that they would ram into each other if both forces did the same tactic and after a few blows and a few kills/fallen allies too back off reform the wall and just push back and repeat the stabbing and after a few fall pull back and repeat? Or would they use other tactics to defeat the wall?
I'm currently in the middle of writing up a more detailed look at this question that won't be done for a few more weeks, but a previous answer I wrote is still more or less how I view the actually ebb and flow of the battle. Most of the initial fighting was done with spears at 1.5-2 metres range, with sections of the line occasionally backing off for a breather or pushing in closer in an attempt to break through the enemy shield wall, before retreating to recover. Rather than the entirety of both shield walls coming together at once, it's best to think of them as bulging towards or away from each other in multiple places.
Beyond this, there was a tactic called the "Boar's Head" formation. Exactly what it was is still debated, although Saxo Grammaticus' complicated three wedge version has been discarded by most scholars and the focus is now on either a single wedge or a square/column formation, depending on whether they scholar prefers Vegetius and the later Scandinavian writers or Tacitus' description of Germanic tactics in the 1st century AD. The only description we actually have of the formation comes from the mid-13th century Norwegian King's Mirror:
If you are fighting on foot in a land battle and are placed at the front of the Boar's Head formation, it is very important to watch the closed shield line in the first onset, lest it become disarranged or broken. Take heed never to bind the front of your shield under that of another.
(I've modified the original translation based on the original Norwegian text for this section - both can be found here - which didn't specifically mention a point, just being at the front of the formation)
It suggests that, whichever formation was used, wedge or column, it was extremely tightly packed. The shields, however, probably aren't locked the way we think of shield walls. At this point kite shields were the primary shields in use, and these were much narrower than a round shield (somewhere around 2 feet/60cm). Two feet per man is probably already as tight a formation as you can get and still have some hope of fighting competently, so the admonition not to let the right side of your shield get trapped under the left of your neighbor's shield is probably a warning not to bunch up and to make sure you have enough room to fight. It's possible that, earlier, when round shields were dominant, the shields were overlapped during this formation in order to make it even stronger, but it's also possible that shields were never overlapped during Early Medieval warfare.
The cause of my doubt comes from multiple sources. The Roman soldiers of Polybius' time (and probably of the early and mid Empire too), for example, occupied a full six feet of space (two feet from themselves, and then two feet between them and the men on either side), while the Hellenistic pike phalanx normally fought with a frontage of three feet per man. Later, in the late Empire and early Byzantine armies, what evidence we have suggests that three feet was the normal spacing between files. And, in the late 16th and early 17th century, pike formations could have as much as five feet per man. Clearly, locked shields or tight formations were not thought necessary for normal combat in any of these periods, so there's no reason why they should be necessary in the early middle ages.
Secondly, the limited visual evidence available that has been interpreted as showing a shield wall has probably been taken out of context. The Osberg Tapestry, the first and oldest example, is clearly depicting some kind of funeral procession and the warriors are most likely in double lines following the wagon. The overlap of the shields comes from either the limitations of the medium and the difficulty in clearly showing the shield side on, or else from an overlap on one side when the warriors marched.
The other major depiction, a 10th century "hogsback" tombstone from Gosforth, Cumbria, is harder to interpret. Although it has been taking for a shield wall previously (see, for instance, the quote from Ian Heath on the site), it could just as easily be a procession. The connection with the dead and the possibility that the stone is a representation of a "house of the dead" raises certain similarities with the funeral procession of the Osberg tapestry. The soldiers are also rendered in profile which, although it could be a limitation of the medium, could also be because that's the intended orientation of the warriors. This makes the interpretation of the tombstone as depicting two shield walls far less certain than has been suggested in the past.
As an additional example of the idea of shields being shown overlapping when the artist intends to show a line of men, look at the Bayeux Tapestry. Given the men in the rear with spare spears on the left hand formation, and the overall density (even with only a small amount of overlap, perhaps a foot and a half of space would be available to each man if the Tapestry depicted a shield wall) and the fact that only the men in the front three ranks and then the distantly spaced rear rank have arrows in their shields, it seems extremely likely, if not 100% certain, that we are seeing a cross section of the English line, as Clifford Rogers suggests, rather than the front rank.
Finally, none of the terms used to describe a shield wall actually mention or imply the locking of shields. "Skjaldborg" means "shield fort". Other references to it being a fence, roof, enclosure, tent, gate, etc. are poetic turns of phrasing, not technical terms and serve as a reminder of what the shield is: protection. Similarly, Anglo-Saxon terms such as "board-wall", "shield fort", "shield wall", "board hedge", "war hedge", etc. are also descriptions of purpose, not of design. Even the glossing of "shield wall" with "testudo" in an Anglo-Saxon to Latin dictionary of the 9th century means little: the testudo was a formation of shields edge to edge, not overlapping. If the Anglo-Saxons, contrary to I.P. Stephenson's suggestion, knew what "testudo" meant, then that may mean they pictured a shield wall as the rims of the shields touching. If not, then that still doesn't mean they pictured overlapping shields, as the interpretation of a "testudo" as being overlapping shields is a modern one, not an Anglo-Saxon one.
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