In 2007, Matthew Barney and Jonathan Bepler began a new collaborative project inspired by American author Norman Mailer's 1983 novel Ancient Evenings, set in pharaonic Egypt. The project was conceived as a nontraditional opera with a series of one-time-only live acts performed across the American landscape over a five-year period. This opera developed as a film titled River of Fundament, which combines documentation of the three live acts with scenes set in a reconstruction of Norman Mailer's brownstone apartment in Brooklyn Heights.

Barney and Bepler reimagine Mailer as his own protagonist who reincarnates three times in three different bodies by magically entering the womb of his wife Hathfertiti. In his attempt at rebirth, Norman must endure the departure of his soul's seven mythological states: the ren or secret name; the sekhem or power; the khu or light; the ba or spirit; the ka or double; the khabit or shadow; and finally the sekhu, or remains. With each incarnation the undead Norman emerges from a river of feces that runs beneath his Brooklyn Heights apartment and enters his own wake.

Imagined as a memorial gathering attended by figures in the New York literary world, the wake takes place inside the Mailer apartment as it is ferried down the river. Guests eulogize Mailer and offer condolences to his widow, while musicians tune and begin play their instruments. Norman's widow and a chorus of guests contemplate the soul's journey as a series of recitatives. As the evening wears on, the wake gives way to a scene of carousing and revelry, in which characters from Ancient Evenings play out their incestuous struggles for power and their insatiable appetite for pleasure as the music gains momentum. Each incarnation of Norman joins the wake for a time, haunting the guests and challenging the ancient undead figures of gods and demigods. He endures two rebirths but fails to be reborn a third time, thus ending his attempt to ascend to a higher, more powerful state. Barney and Bepler have adopted critic Harold Bloom's suggestion that Ancient Evenings was a thinly-disguised allegory for Mailer's literary ambition. The powerful pharaoh Usermare evokes the spirit of Ernest Hemingway and engages Norman's three incarnations in a struggle for dominance.

In a parallel narrative, River of Fundament replaces the body of Norman with the body of an automobile in the American landscape. Three generations of American cars act as vehicles that carry the narrative: a 1967 Chrysler Crown Imperial (known for its crashworthiness) is transmogrified into a 1979 Pontiac Firebird Trans Am (known as the last high-performance engine of the original muscle-car generation) and finally into a 2001 Ford Crown Victoria Police Interceptor (known for its tireless service in the U.S. government fleet).

The automobiles' story begins with REN, a live performance staged at a car dealership in south Los Angeles. A 1967 Chrysler Crown Imperial undergoes its first death and is prepared for rebirth as a 1979 Pontiac Firebird Trans Am. The second performance, KHU, unfolds along the River Rouge and Detroit River. KHU brings the Chrysler back to its birthplace Detroit, a city rich in minerals, iron, and limestone, built upon the vast expanses of salt beds beneath Michigan. KHU sees the Chrysler Imperial dismembered and melted in five monumental furnaces. BA, the final live act, takes place at locations along New York City's East River, culminating in a battle at a dry dock in the Brooklyn Navy Yard. At the conclusion of BA, the automobile is further transformed into the 2001 Ford Crown Victoria.

Set amid the American landscape, River of Fundament uses the language of modern industrial processing and recycling to tell the story of its automobile protagonist, alongside characters deployed from CREMASTER 3 (the Entered Apprentice and Entered Novitiate) and the Egyptian pantheon activated by Mailer (Osiris, Isis, Set, Nephthys, Horus, Anubis, and Khepera). The mythologies inherent to these characters are met at each site with a set of local mythologies, symbolisms, and indigenous musical traditions as diverse as Native American, American, Mayan, and Celtic. Each performance employs local talent, while the set of characters inherent to CREMASTER 3 and Egyptian mythology continue to evolve and reappear, pervading the transformation of the automobile protagonist as it endures the seven soul states toward the journey of its three embodiments.

Sculpture is generated with each transformation of the automobile. The recurring motif of a graduated ascent to power is articulated in the material language of the metals and minerals that take form in sculpture. Base elements — zinc, sulfur, iron, copper — give way to yellow metal alloys — bronze and brass — that emulate, but fail to reproduce, the quality of gold.

River of Fundament is characterized by musical performances directed according to the logic of the narrative: the story unfolds sculpturally, cinematically, and musically. Bepler uses speech and ambient rhythms as compositional elements, in addition to more traditionally-scored arias and recitatives. Sounds inherent to the landscape or action become part of the musical texture of the film, such that the setting itself becomes a musical instrument. The site-responsive nature of the music is also developed through the use of local musicians, both professional and amateur, whose performances further establish a sense of place in each scene.

Primarily excerpted from Mailer's Ancient Evenings, the libretto also includes historical rites from the Egyptian Book of the Dead and The Pyramid Texts, along with texts from American authors Walt Whitman, Ralph Waldo Emerson, and William S. Burroughs, offering a confluence of meditations on the timeless concerns of mortality and regeneration.