Although many are convinced that Leonardo's Mona Lisa Italy has been stolen, in reality it is legitimately France.
The confusion arises because, actually, Napoleon's soldiers plundered our country (and not only) the many works of art, only partially returned after Congress of Vienna (1815).
But for the Mona Lisa it is not so (see also: https://www.pilloledistoria.it/2575/notizie/test-dna-monna-lisa).
It was the same Leonardo fact, to carry the portrait of Monna Lisa in the country beyond the Alps, where is the re Ferdinand I bought.
The figure for it was mind-boggling: ben 4000 shields of gold, roughly the equivalent of two years' salary for its author.
I however Napoleonic soldiers, They stole the manuscripts of Leonardo known as Codes of the Institute of France, never returned (photo: ilgiornale.it).