[heraclius]

The Byzantines not call themselves Byzantines; they considered themselves Roman. See a helpful answer on Reddit¹ which notes an episode in which the Byzantines imprisoned an envoy for calling their emperor that of the Greeks. It would of course be obtuse to call the Byzantine Empire the Roman Empire, but the renaming was after 1453.

¹ https://www.reddit.com/r/AskHistorians/comments/ak435w/did_t...

[rgblambda]

During the Greek war of Independence I believe, children on a small island in the Aegean ran out to see the Greek soldiers who landed. A reporter asked them "why do you want to see them". The children replied "to see what the Hellenes(Greeks) look like". The reporter confused said "but you are Hellenes". The children laughed and said "no, we are Romanes".