There's no composer quite like Iannis Xenakis, who died in 2001. A pioneer of electronic music, a musical and mathematical visionary who invented ways of mapping scientific processes on to musical composition, he created some of the most defiantly individual music ever written, connecting the worlds of ancient Greek philosophy with contemporary composition. The South Bank's weekend-long celebration of his music, Architect in Sound, was a thrilling experience - an explosion of astonishing virtuosity and sonic power that was as exhilarating and overwhelming as a force of nature.
Perhaps it's no surprise that Xenakis's music should create the elemental effect of a piece such as Shaar, for 60 strings, which the BBC Symphony Orchestra performed with conductor Jac van Steen. The music built into a massive wave of sound that knocked you out of your seat, as if the players had fused together to create a gigantic meta-instrument. Instead of melodies and harmonies, Shaar - like so much of Xenakis's work - is made from glissandos and piles of crunching dissonances, a music as geological as it is human.
Born in Romania but raised in Greece, Xenakis was a man for whom nature was a continual inspiration. It was the violent beauty of the natural world that attracted him. As his daughter relates, on his annual holiday in Corsica, he would pilot his kayak into the teeth of a Mediterranean tempest, revelling in the extremes of nature unbound. Yet he was formally schooled and uncompromising: Xenakis was also a trained architect, who worked for Le Corbusier's Paris studio in the 1950s.
He used stochastic mathematics to compose one work performed here: ST/10, a piece of gritty complexity for an ensemble of 10 players. In the London Sinfonietta's performance under Diego Masson, the piece was gnarly and challenging, turning each performer into a separate layer of musical strata - evident in the steady march of the harp part, or the garish shriek of the clarinet.
For all this scientific rigour, the weekend also revealed the visceral, physical side of his music, and its communicative, moving qualities. In 1944, Xenakis was horrifically injured while fighting for the Greek resistance against the British occupation. He lost an eye and the left side of his face, and his sense of political injustice never left him. In 1967, he dedicated Nuits, for 12 singers, to "unknown political prisoners", and the piece is a shattering scream against inequality and tyranny. There is no text, but in the BBC Singers' performance the music's grunts, whistles and otherworldly extremes of high and low gave voice to primeval pain and suffering.
Yet it was the cathartic, uplifting power of this music that will live longest in the memory. In the Purcell Room, pianist Rolf Hind played Evryali ("The Snake-haired Medusa"): the piece has such astounding energy that it seemed to explode into another dimension of musical expression. It was as vertiginous for us to listen to as it must have been for Hind to play.
The most extreme music of the weekend was pianist Nicolas Hodges's performance of Eonta ("'Beings"), with the brass players of the London Sinfonietta. This piece, written in 1963, still sounds like a musical message from another planet. After a ferocious opening solo, the brass players walked across the stage to play their instruments into the strings of the piano. Part obscure ritual and part hurtling, virtuosic fantasy, the music did not let up in intensity until the final mysterious brass chords.
The performance was cheered to the rafters by the huge and appreciative audience who followed this whole weekend: a lesson, surely, that the braver the programming, the bigger the audiences.
