how a Roman emperor crowned?

[Lord Hobbers]

I'm most interested in the time of Hadrian and his successors to Commodus

As is my understanding, emperors of the Principate were not 'crowned' in the modern sense that we understand today. The symbol of ancient kingship was the diadem, which the Roman emperors did not wear, and any form of headwear in Rome was not associated with kingship or power; their wreaths symbolised military achievements and, in theory, could be awarded to anyone, not just the emperor.

Status in Roman society was usually displayed through one's clothing, for example, the use of purple stripes on tunics and togas. I'm pretty sure there are references to emperors, when they are proclaimed by their troops, being draped in a purple cloak or mantle, which is probably why becoming an emperor is sometimes referred to as "assuming the Purple" or "to take the Purple". I think under Roman law, only emperors were supposed to wear purple (though in practice this wasn't really adhered to), so if there was any form of ceremony, it would probably involve them putting on a purple toga maybe. However, I don't believe there would have been a ceremony in the same way we have a coronation; they would merely be confirmed in the role at a session of the Senate and that would be that.

Though, of course, I would be fascinated to hear if there was any evidence to suggest a ceremony of some sort.