VLPP - History of the "Pannonian Hat"
Although this piece displays an obverse portrait unlike any other on Imperial Roman coins, the headgear was worn in the 4th century AD. Click on the image in the table to open a larger version.
In order to get more information on the background of the Pannonian cap itself, I contacted Robert Vermaat, a gentlemen who is a member of a Roman military re-enactment society, Fectio. Here he is, wearing an example of a Pannonian cap, or Pilleus Pannonicus:
Mr. Vermaat had these comments on January, 21, 2004:
"By ‘standard’ headgear [when describing the cap] I am of course talking about ‘military standard’, and as such it is a relative term. We don’t know anything about Roman uniform, not even if such a thing existed during the full extent of the Empire. The pilleus, however, is the only form of headgear depicted on any of the scarce images of what we think are soldiers. The general conclusion is that the Pilleus Pannonicus was worn by soldiers in general, either because these were issued by the state, or as a form of military fashion.
The first of these pillei to appear on Imperial heads is one said to have been worn by the Emperor Carinus (283-5 AD), "to hide his baldness in front of the Sassanid ambassadors" (Synesius of Cyrene, De Regno, 12 OP, m66, 1804). The spread of this Pannonian headgear may well be explained by the new elite status of the Dalmatian cavalry units (Equites Dalmatae), whose role in the military success after the crisis of the mid-third century lead to their dispersal over other armies. It can be assumed that these troops wore the Pilleus Pannonicus as their local headgear, and that this fashion spread as a result of the elite status of these troops.
A similar distribution of such an item can be observed of the Plumbata mammilata or ‘lead-weighted throwing dart’. This item is said to have originated in two Illyrian units, but it spread throughout the Empire during the exact same period. I think we may safely think of the pilleus as a military-inspired fashionable piece of headgear of Illyrian origin.
What concerns me a little in your coin is the lack of regalia on this particular piileus. You are, in my opinion, right to suppose that either a diadem or a wreath may have adorned the Imperial pillei, or any form of adornment which would have set it apart from the ordinary military ones. The pilleus was not some form of regalia by itself, even though Sumner thinks it’s shape was influenced by the Persian tiara (Sumner, g. (2003): Roman Military Clothing (2): AD 200-400, (Osprey, MAA 374), p. 37).
However, it could be said that by depicting an ordinary hat, Constantine meant to identify himself with the ordinary soldier.
By the way, your identification of Maximian (or Constantius I Chlorus?) is by no means a given. This magnate could in fact be anyone, and the connection of the building to Maximian is not secure – a quite accepted explanation of his name would be that he gave it to the (unnamed) owner. However, the presence of soldiers on the mosaic would lead me to suppose that the mosaic shows at least an official with military tasks. But it is a possibility."
A comment from Dr. Sidrys, received on February 6, 2005:
Regarding Pannonian hats, my personal opinion, having seen the mosaic at Piazza Armerina, and having lived in the former USSR for a few years, is that they were rigid forms of felt, rather than animal fur, as suggested by the photo of (Mr. Vermaat) in your website. The mosaic artists or sculptors would have been sufficiently skilled to depict the irregular details of a fur-skin hat. Instead, they depict all of the Pannonian hats as rigid cylindrical shapes, very similar to a military felt hat.
My comment: Having the coin in hand, the description of "rigid felt" would fit well. The headgear pictured on the coin is textured, and if it were life-size, would most likely look similar to felt vs. fur.**Note to self - Find image of RIC IV, Part I, 10 (aureus of Clodius Albinus in 194-195) with reverse type Saeculum Frugiferum, bearded, wearing fez, in robe reaching to feet, enthroned left, flanked by sphinxes right and left, holding up right hand and holding grain ears in left.