I was reading about how Caligula ordered the death of Ptolemy of Mauretania on stephaniedray.com and she states this:
"We are traditionally told that after having been invited to Rome in 40 CE, Selene’s son appeared in the arena with his cousin, the emperor, while wearing a splendid cloak. This was undoubtedly a purple cloak because Mauretania was famed for its Gaetulian purple dye industry. The Mauretanian royal family would have flaunted that purple for all it was worth. However, purple was the color of royalty. Certainly, as Cleopatra VII’s grandson, Ptolemy would have had more royal blood in his little finger than the emperor had in his whole body–and that may have been the problem. As the legend goes, Caligula didn’t take kindly to the idea that anyone should wear royal purple better than he did, and descended upon his first cousin in a murderous rage."
How accurate is the bolded sentence? I thought Caligula himself was a melting pot of royal blood
First, it's dangerous taking claims from writers of historical fiction seriously. Some can be very good, but history is always going to cave to the needs of the narrative even in the best cases. I've never read Dray's books so I can't comment as to how good they are.
Second, I wonder about the definition of the term "royalty." Ptolemy of Mauretania was the descendent of the last of the Greek royal lines; a dynasty of over three hundred years. Rome had nobility, but hadn't tolerated royalty for some 700 years. I would describe Caligula as a melting pot of celebrity myself, and that's a rather different thing. Caligula was a descendant of Augustus through Julia, a Claudian through Drusus, and a descendant of Marc Antony through Antonia. Claudians were a very ancient aristocratic family; Augustus and Antony obviously the most important politicians of their age, but none of them were "royalty." Even if they were, we're talking about 80 years max you could speak of a Julio-Claudian dynasty, compared to the Ptolemies' more than three centuries.
But again, we're talking about a fiction writer here. It might be useful to look at the source material. Suetonius' Caligula, 35:
After inviting Ptolemy, whom I have mentioned before, to come from his kingdom and receiving him with honour, he suddenly had him executed for no other reason than that when giving a gladiatorial show, he noticed that Ptolemy on entering the theatre attracted general attention by the splendour of his purple cloak.
Suetonius doesn't say anything about "royalty" being an issue. It seems like that is supposition on Dray's part.