Decasia was commissioned by the Europäischer Musikmonat 2001 for the Basel Sinfonietta. Filmmaker Bill Morrison, a member of the Ridge Theater company which has often collaborated with Bang on a Can composers, was asked to create a visual component for the project. Morrison turned to deteriorating archival film footage of various subjects, ranging from The Man Who Could Not Sleep, a 1915 Edison production, to 1927 Fox Movietone newsreels found at the University of South Carolina.

"I had recently found what were to become the seed images of Decasia - the nun sequence and the boxer - while rummaging through an archive in South Carolina," Morrison wrote. "I suggested that we make decay the theme of the piece, and that the piece be called Decasia. Michael took this to musical extremes I couldn't have dreamed of, writing a decaying symphony, to which I edited these images.

"The images can be thought of as desires or memories: actions that take place in the mind. The filmstock can be thought of as their body, what enables these visions to be seen. Like our own bodies this celluloid is a fragile and ephemeral medium which can deteriorate in countless ways. The nitro-cellulose base gradually returns to the elements that comprise it: cotton, nitric acid, and camphor. The images deform and coalesce throughout the length of the film, appearing to melt, burn, drip, or tear away from the base. This is a natural phenomenon. I chose only those images where this deterioration had happened over time, while stored in archives. I did nothing to accelerate the process. Like the film, our bodies will eventually be reduced to what essentially forms us. What we contain, our thoughts, dreams, and memories, will be reprised as something new and, hopefully, more lasting."

"The musical inspiration for Decasia came from the very earliest visual material that Bill Morrison showed me when we began discussing the creation of this work," Gordon wrote. "I was overcome by the sensual beauty of the film, and immediately started to think about decay in musical terms. What would an equivalent to the look of decayed celluloid be in music?

"The image that came to mind was that of a neglected piano sitting untuned for 100 years. For Decasia, I 'invented' four terribly out-of-tune pianos that are heard at the very beginning and throughout the entire piece. But the bigger challenge was the symphony orchestra, for which Decasia is written. To create a sound in the orchestra that would match these four special pianos, I de-tuned the orchestra, so that most of the time, half of the orchestra is playing just slightly out-of-tune (1/8th of a tone higher or lower). I also ask for a continual sliding of pitches from one note to the next, which also gives a constant feeling of pitch instability."

For the Musikmonat premiere, Ridge Theater staged the performance with film projections on a scrim. Morrison's film version of Decasia was premiered at the 2002 Sundance Festival and is available on a Plexifilm DVD.