Why did the scutum have a horizontal grip?

[M. Demetrius]

Well, it's fun to discuss what we think about all the aspects of what we often call reenactment, but what really matters in the end for those who want to "get it right" is what the ancients did. Someone might decide that a particular angle of scutum grip feels right to their hand, but did the Romans actually use that grip? Were there tactics what we imagine them to be? Sometimes those questions just simply can't be answered.