Crista Transversa

[M. CVRIVS ALEXANDER]

I would add to the above posts that the tombstones do not seem to show "transverse cheek pieces." They show frontal views of the helmets, presenting the cheek pieces - and the crest - the way they actually seen as you look at the helmet from the front (see the pic). This is particularly evident from the tombstone of of centurion T. Calidius Severus, which depicts a somewhat 3-dimensional image of the helmet. The cheek pieces curve along with the bowl from the sides to the front. The crest, however, is a plain transverse crest. It would take an immensely wild stretch of imagination and disregard of other items presented on the tomb to see this crest in a "front-back" position.

The references from Vegetius, in this case supported by the above archaeological data, provide IMO a strong piece of evidence.

Some of the found helmets have a slot for a crest holder, but have no specific attachment devices (e.g., Itallic D featured on the photo). Some of those helmets could have been used by centurions, who could attach their transverse crest w/o any extra devices on the bowl - see the same pic.