Testudo

[Tarbicus]

So as long as the shields were of equal size, then the person who was holding the shield on top would be ok. But, if his shield was a bit smaller, symetrical or not he may have a problem. I'm not sure we know how uniform the scuta were within a century/cohort.

There's a primary reference to a legionary being either punished or castigated for having a different scutum to the rest of his unit, as he wouldn't be able to protect his neighbours. Now this whole discussion of the testudo puts a very focused reasoning behind the reaction to his shield.