Da Vinci diamonds, at 722 carats, could have represented more than $80 billion in valuation, or more than £30 billion in today's money.
Many of them still exist - including those at Baselworld, Monaco and The Hague in The Netherlands. But their ownership now is shrouded in mystery.
"If the ownership was known to the public, it would have been seen as a public nuisance that should have been concealed," said Paul de Zeeuw, emeritus professor of art and society at the Royal College of Art, UK.
Yet the rumors, that the gemstones were sold for $7.4 billion to $11 billion, have endured.