Lol, Persians? 
Also, in the late roman times, the whole army concept changed. Legions no longer garrisoned the line itself (such as the Rhine Limes), but were held back in centres away from the frontline, ready to reinforce positions in times of need. As such, it might have been more useful to shift to shift to lighter equipment?
Perhaps, but then part of the strength of the Roman military had always been the ability to deploy quickly. There is a good reason for their roads, and their logistical abilities where very well developed.
