The layers of lore that encrust the ravishing unfinished Requiem Mass keep re-forming, no matter how many times they are scraped off. Mozart did not, as Amadeus would have it, compose the piece for a mysterious figure who appeared at his door dressed like the Grim Reaper. He also did not have intimations that he was composing his own funeral music. The truth is paltrier: the Requiem was commissioned by a Viennese aristocrat who liked to get others to write music he would then peddle as his own. Mozart died before he could turn it in, and some of the piece's most shuddering sections were actually written by a friend. But the music needs no mythology to sell it. It is as dramatic, visceral and lush a work as any that was ever penned to rattle souls in the concert hall.