In spite of what Hollywood would lead you to believe, Persians did NOT parade around half-naked, wearing nothing but gold chains. Ahem. As with most desert-dwellers, coverage was actually crucial to keep the burning sun from boiling them. Persian men wore what was fairly typic everywhere in the ancient world, starting with a basic tunic, then adding a more decorative over-garment. In the case of Xerxes, it’s often classified as a robe (being royal and all), and on more than one occasion we see reference to the men wearing wraps translated as shawls to fend off a chill.
I had some difficulty figuring out what they wore for shoes, but the information I finally stumbled across said they just wrapped leather strips around their feet and tied them above the ankle.
Herodotus does go into detail about how the armies are decked out, and I found it rather strange that instead of any kind of metal helmet, the Persians wore felt caps.
(Photo is artist rendition of Xerxes’s soldiers based on Herodotus’s descriptions)