With the slow but unstoppable force of a juggernaut, the UNESCO Convention for the protection of cultural property, approved on November 14, 1970 — after which year the acquisition of antiquities ceases to be legitimate unless accompanied by an official export license — is reconfiguring the market. Not all nations subscribe to the Convention, and those that do, like the United States, may not enforce all of its provisions. Yet several factors are combining to make the Convention increasingly effective across most Western countries (with some notable exceptions, such as Switzerland). One is the weight of public opinion, led by scholars who deplore the massive loss of historical documentation that the unrecorded looting of archaeological sites entails and the destruction of a huge proportion of buried art treasures resulting from the crude methods to which commercial diggers resort.

A second factor, more powerful than concerns for mankind’s buried historical and artistic heritage, contributes to the adoption of the 1970 UNESCO Convention as a de facto rule of thumb. Growing numbers of buyers feel that at some point in the not-too-distant future, the Convention will be widely adhered to. Then, costly antiquities first bought after 1970 will become hard if not impossible to sell, and their commercial value will nosedive.

Proof that auction houses have become acutely aware of the problem is provided by the policy that is quietly followed at one of the two international companies dominating the auction market. A few months ago, as I congratulated Florent Heintz, international head of the antiquities department at Sotheby’s, about the number of ancient Roman sculptures ensconced in the cultural past of Europe that he has been handling of late, the expert replied, “This is what we are looking for right now.” The latest antiquities sale held at Sotheby’s New York, on June 7, certainly bears out Heintz’s words.

The four top lots in the auction had all reached Western Europe by the 19th century. The highest price, $902,500, greeted a Greek marble stele from the third quarter of the 4th century B.C. The funerary monument is carved in low relief with the figure of a young man clutching a dove in his right hand. A dog stands on its hind legs, hoping to snatch the bird. A certain rigidity about the sculpture is not fully compensated for by the rendition of the subtly wistful expression of the deceased youth, who smiles ever so faintly.

Fortunately, the history of the stele made up for any such weaknesses. The story of its discovery was recounted in 1877 in the journal of Classical studies Parnassos. The marble was dug up in Athens on June 27 of that year, on the grounds of the property of a certain Michael Melas. In 1900, it was described and illustrated in Volume II of the corpus of Attic Funerary Reliefs compiled by the classicist Alexander Conze. Other publications followed in the late 20th century, including Christoph W. Clairmont’s Classical Attic Tombstones, Volume I, in 1993. While on loan to the Metropolitan Museum of Art between 1964 and 2011, the gravestone acquired an aura that further contributed to its performance. At $902,500, the stele far exceeded the $500,000 high estimate.