An early Banksy work painted on the side of a festival worker's trailer has fetched £445,792 ($676,668) at an auction in Paris.
Silent Majority, painted during the 1998 Glastonbury Festival, shows soldier-like figures landing on a beach with a speaker in an inflatable raft.
Its Norfolk owners say it "depicts the ...rave and hip hop scene of the time".
The work is unusual for a Banksy piece, as it is largely freehand with little use of stencils.
Auction house Digard said it was thought to be one of the artist's oldest works.
The metal piece, painted over three days outside the festival's Dance Tent, measures 2.4m (7.8ft) by 9.9m (32ft).
Its message reads: "It's better not to rely too much on silent majorities ... for silence is a fragile thing... one loud noise and it's gone."
The elusive graffiti artist's team has provided a certificate of authenticity as part of the auction lot. It was painted in collaboration with fellow Bristol artist Inkie.
The owner, who prefers to be known by his first name, Nathan, said he organises infrastructure at festivals and lives in the trailer.
He said Banksy approached him in 1998 - before he rose to fame - to ask if he could use it as a canvas for a piece commissioned by the festival.
Nathan agreed, in return for some tickets and his expenses.
Now he says he has no definite plans for the proceeds although he may choose to build a house.
Street art specialist Mary McCarthy said the piece was "quite special" as an example of a Banksy work which did not rely heavily on stencils.
"This one really is a rare piece," she said.
It was one of more than 150 "urban art" pieces auctioned on Monday including work by artists Jeff Koons, Damien Hirst, Pure Evil and Conor Harrington.