Cannae - why bother with the cavalry?

[Timianus]

I'll also throw in another, quite possible and simple reason why the Roman deployment was as it was...

The Romans deployed their armies with legions in the centre and cavalry on the wings.

Nothing more and nothing less.

Yes, it is interesting that when describing the battles against the Welsh, the Anglo-Saxon Chronicle states that the Welsh arranged themselves "in the roman order" with cavalry on the wings, infantry in the center, and archers behind. This does seem to have been the "default" formation throughout the ages.