Krzysztof Penderecki‘s Threnody to the Victims of Hiroshima (1959) was composed for 52 string instruments. At first it seemed to the composer a mere experiment in form, counterpoint, and unconventional scoring — the original title of the piece, a possible homage to John Cage, was 8’37″ or 8’26″ — but Penderecki was then “struck by the emotional charge of the work. … I searched for associations and, in the end, I decided to dedicate it to the Hiroshima victims.” It has since become a classic of contemporary music.
The Wikipedia page dedicated to the composition has more about its formal qualities. Below, an “animated score” version of the piece, as it is performed by the Polish National Radio Symphony Orchestra. A brief video detailing the various symbols used in the score is available here.