Roman Emperors and the \"King\" title

[Epictetus]

As you probably know, Gibbon writes "medals" when he means coins

Thanks! Actually, I wasn’t entirely sure what he meant when he used that term. In some contexts it seems clear, but I had thought he tended to use it as a catch-all for coins or non-monetary tokens.

Regere and rex are from the same root. "Regi" is probably the dative of rex. Since "Hannibaliano" is also in the dative, it would fit. "Fl(avio) Hannibaliano Regi" "To Flavius Hannibalianus, King". If he used the coins outside of Roman dominion or in an attempt to secede as King of Pontus or King of Kings, it would work; for a Roman emperor, it is certainly odd.

Constantine’s succession plans seem almost indecipherable to me. Did he expect all of his heirs to rule jointly and equally, or were some subservient to others? I’m wondering if there were shades of Diocletian’s tetrarchy here. Based upon Hannibalianus’ titles, it seems like he was (or was claiming) one of the highest positions, which previously would have been titled “Augustus.”

If no one else can think of any other instances of “Rex” being used, he must really have been unique.