“These items aren’t for sale,” the museum director snootily informs movie supervillain Erik Killmonger in the Black Panther. The items include Benin bronzes, sacred artefacts that are also stunning works of art. They were looted from Nigeria by British armed forces in 1897. Irony aside — “you think your ancestors paid a fair price?” Killmonger taunts — the curator’s comment was prescient. As calls for repatriation grow louder, Benin bronzes are becoming unsaleable on the open market.

Just last month auctioneers Burstow & Hewett withdrew a Benin bronze because of “uncertainty over provenance”. That euphemism relates both to authenticity and the ugly tale of how Benin was pillaged.

Britons seized more than 10,000 artefacts in the invasion of the West African kingdom of Benin. More than 1,200 items were fine bronzes, proving to the wider world that Africans could produce sophisticated figurative art.

Pressure from Nigeria, Africa’s most populous country, means curators and collectors are wrestling with whether to hand back Benin treasures. The controversy is part of a broader “culture war” over colonial-era art that has triggered departures on UK museum boards.

The British Museum, the inspiration for the cinematic Museum of Great Britain, holds about 900 Benin artefacts. The roll call of other holders spans more than 150 museums, universities and private homes.

Two charts; Sized circles showing selected pieces, by sale price (€) for Benin bronze sculptures and bar char showing the ocations of Benin plaques looted in 1897 by museum

Soldiers and sailors were among the first vendors of Benin bronzes. Dan Hicks, author of The Brutish Museums, points to the Pitt Rivers Museum’s 1899 purchase of a plaque for the princely sum of £4 and 3 shillings. A century or so later, prices had climbed into hundreds of thousands. The Ohly head then went for a reported £10m.

Precious few buyers are now publicly bidding for contested African artworks. On the face of it, this implies the value of Benin bronzes is precisely zero. It would be more accurate to say the best of the sculptures are priceless.

Some institutions are tentatively beginning to return objects to Nigeria. Aberdeen University plans to send back a bronze head purchased at a Sotheby’s auction in 1957 and theoretically valued at £500,000. Private collector Mark Walker has handed back a pair of bronzes.

The British Museum has not agreed to transfer ownership of bronzes, citing the value that vast and varied collections of art have to the public and scholars. It has pledged to lend Nigerian objects for display in a new museum in Benin City.

Wrangling over the form and allocation of display rights will rumble on. But one way or another, after spectacular rises and falls in value, many of the Benin bronzes will be heading home.

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