Of the nearly 4000 portraits now known from Palmyra, thanks to the work of the Palmyra Portrait Project, twenty-six portraits can be distinguished, representing a small but important group, all sharing one trait: they depict men with Roman type swords. The type of swords, clothes, and other attributes separate them from the men with military equipment shown in connection to caravan or trade scenes, and make certain their association with the Roman army.
Bobou et al. (Wed,) studied this question.