It was the BBC Proms that started the idea. Back in 1997, they presented Yevgeny Kissin in a solo piano recital that put the pianist in the middle of the arena surrounded by a 5,000-plus audience. The event was a big success, but only one musician since has dared repeat the feat, the Chinese pianist Lang Lang when he gave his solo Prom two years ago.
Obviously, he relished the challenge. Describing the hall as the modern equivalent of ancient Rome's Colosseum, he returned on Friday to give another recital outside the Proms season under the same conditions - performer as gladiator, cheered on by a near-capacity audience of his fans.
The programme was solid and serious. Today's audience may not want to see Christians thrown to the lions, but they might have expected some red-blooded entertainment. Instead, Lang Lang, of all pianists a showman first and foremost, defied expectations by giving the crowd a fairly sober selection of Beethoven, Albéniz and Prokofiev - no tasty titbits until the encores.
His two Beethoven sonatas - the early Op 2 No 3 and the middle-period "Appassionata" - made a concentrated first half. In Mozart, Lang Lang has often shown himself to be on his best behaviour and his Beethoven here was similar, sturdier as the music demands, but free from extremism except in the far-flung contrasts of the "Appassionata". The calm, patient slow movement of the Op 2 sonata was especially effective.
In the Albéniz, the first book of Iberia , the gentle touch was almost too subtle, and people at the top of the hall must have been straining to hear. But there was no problem in Prokofiev's Sonata No 7, which started off bold and percussive, and held off sensationalism until it collapsed into incoherence in the final excited minutes.
The encores were all Chopin. Here, at last, he played to the gallery - the Etude in A Flat, nicely poetic, followed by some wildly over-the-top hammering in the A Flat Polonaise and E Major Etude. Overall, however, this was one of Lang Lang's most considered and mature recital appearances in London.
Whether the audience appreciated it is another question. The constant flashing cameras suggested they only came with star worship in mind.