Tropaeum Traiani versus Trajans Column

[drsrob]

Well, there IS a depiction of an auxiliary on TC carrying a curved scutum, and the shield cover from Roomberg is wide enough for a curve-faced shield.

There were also cohors 'scutata'. Whether they used a curved shield is arguable as all shields are in effect 'scuta'. Interestingly IIRC both scutata cohors were from Spain, and were equitata.

Cohors II Hispanorum Cyrenaica scutata equitata
Cohors I Lusitanorum Cyrenaica scutata equitata

Erant, ut supra demonstratum est, legiones Afranii tres, Petreii duae, praeterea scutatae citerioris provinciae et caetratae ulterioris Hispaniae cohortes circiter LXXX equitumque utriusque provinciae circiter V milia.[...]

During the Civil War the auxiliary cohorts recruited from Nearer Spain were still armed with caetrae while the cohorts from Further Spain were equipped with scutae which in these circumstances would surely refer to Celtic shields and not to Roman ones.
Imo therefore the title Scutata in imperial cohorts indicates no other shield than that of ordinary auxiliary cohorts. As we know of no cohortes caetrati from imperial times the term is probably simply a relic.

As far as reliability is concerned:

One thing I noticed on TC is that all auxiliaries are equiped with breeches, short tunics and short mail shirts whether they are infantry or cavalry.
On grave stones however auxiliary infantry is equiped much the same as legionaries. I.e. waist belts with sporran, long tunic, short swords etc. There breeches and short tunics and mail shirts are only found on cavalry.

Now the only auxiliary troops stationed in Rome were the equites singulares Augusti. Imo Italian sculpturers must have considered this barbarian dress and would have assumed that all auxiliaries as non-Romans would have dressed the same.