Armor of the Divine Triad : lamellar armor

[Nathan Ross]

the shape of the helmet, not really in use by the time of Severius Acceptus, makes me think that this stele is just an evocative way of depicting this centurion.

This style of helmet is actually quite usual for the 3rd century and later - in visual depictions anyway. Helmets of similar appearance turn on on grave stelae, the Dura Europos murals and imperial sculpture. Rather than being 'evocative' or the product of classicising 'artistic license' I would see it as entirely realistic, like the rest of Acceptus's gear - the spatha and belt fittings, for example.

A friend alerted me for this in the crypt of the "Abbazia di San Domenico Abate a Sora", Italy

Thanks - never seen that before! It does look quite similar to the Acceptus version...

Perhaps the undergarment is unusual in its design, and was painted to reflect some rank distinction?

Or perhaps it isn't an undergarment? We might assume that padded or quilted 'armour' would be low quality, but perhaps this is actually quite a prestigious item, and does indeed reflect higher rank?

I think the belt is a quite ordinary 3rd-century ring buckle belt, btw, not an officer's sash.