Information and descriptions: Statues of Mithras slaying the bull (Tauroctony) from the British Museum (inv. 1805,0703.270; Townley Collection; CIMRM 593-594; first century CE), Ny Carlsberg Glyptotek, Copenhagen (inv. 716; CIMRM 596), and Ostia Antica Museum (inv. 149; CIMRM 230). Mithras himself is pictured wearing a “Phrygian” cap, a baggy tunic to above the knees and a cloak or cape. Less important for our purposes here, the standard bull slaying scene more broadly is a depiction of the universe in the form of various constellations (bull, scorpion, canine, snake, etc).
Comments: The mysteries of Mithras as practiced by soldiers in the Roman army have very little that is actually Persian about them, but the image of the god himself is the epitome of a Roman representation of a Persian. The idea that the god was a foreign, Persian deity is what mattered a lot. As a result, we get a stereotypical picture of what a second century CE Roman artist (echoing previous iterations of the bull-slaying scene) thought a Persian would look like in terms of clothing. Central here are the so-called “Phrygian” cap (a conical hat tipping over at its tip, which is now missing in the Ostian example since it was a separate piece), the belted loose-fitting tunic with folds (coming down to above the knee), and the cloak or cape tied around the neck and flowing back. Typical of depictions of “barbarians,” particularly northern or eastern ones, is the somewhat wavy or wild and unkempt hair.
Source: Photos by Harland, except for the first from the British Museum by Carole Raddato
(all licensed under CC BY-NC-SA 4.0).