what was the function of the Roman cavalry?

[xrubio]

An attack from the rear would succeed if the attention of the infantry was focused to the fron, already a confused situation at Cannae, once the the heavy phalanx had started its flanking attack! The rear would have been barely in the position to smartly wheel about to face the new threat.

I'd have thought it simple for the men to turn and face the cavalry, especially as they were Triarii and highly experienced? I find it difficult to think that there would be no response, and for the cavalry to 'sneak up' on them.

In fact attacks from the flank seems more effective than attacks from the rear along all the history of warfare, I think, "rolling up" the whole line of infantry. Maybe it is more complicated to defend, given that infantry must realign the face this threat.

Xavi