With an auction of antiquities coming up at Christie's New York, on December 9, Looting matters highlights the perennial difficulty of provenance.
He is discussing a beautiful late Roman - late fourth century/early fifth century - silver paten which shows the Traditio Legis. It could be yours for US$600,000 - $800,000. Actually, the way recent auctions have been going, it could be yours for less than that.
But he is depressingly right about provenance. The silver paten is "the property of a private US collector"; a Byzantine silver cup is "property of a gentleman"; and a Byzantine gilt bronze plaque is "English private collection, circa 1980". None of these descriptions are remotely useful.
Image copyright Christie's also with a much higher res image.