But the Rosetta Stone is an artifact of the rulers of Egypt, who at that time were the Ptolemaic Greeks, who aren't around to claim it, so possession nine points of the law.
The artifact reflect Egyptian culture. the ruler may have been of Greek descent but they styled themselves as Egyptian Pharaohs
And as for the cliche “Possession is 9/10ths law” I would suggest you NOT try it in any courtroom (even those with Democratic appointed Judges) anywhere in the civilized world, whether they have Common Law, Hindu Law, Moslem Law, Napoleonic Law or any established body of law.