This Labor Day, Sept. 5, is also the 100th anniversary of the premiere of “Intolerance,’’ director D.W. Griffith’s sprawling silent-movie epic. Crosscutting between historical conflicts (Babylon and Persia, Pharisees and Jesus, Catholics and Huguenots, modern-day capital and labor), the three-hour epic and its $2 million-plus budget defined Hollywood extravagance. Griffith’s previous production, the sweeping (and flagrantly racist) “The Birth of a Nation,’’ was a runaway hit, but “Intolerance’’ flopped. Today, it is recognized as groundbreaking: strikingly experimental, inimitably grandiose. It also opens a window into the rich and, often, historically hazy world of silent-movie music.

“Intolerance’’ came with its own score, performed by a live orchestra at screenings, by Joseph Carl Breil, a one-time operatic tenor who made a career conducting and arranging in theaters before turning to film, including music for “The Birth of a Nation.’’ True to common silent-era practice, Breil’s “Intolerance’’ music mixed original cues, popular airs, and excerpts cribbed from Beethoven, Wagner, and Verdi. Uncommonly, however, Breil’s score survived, deposited at the Library of Congress along with a book of 2,203 frames from “Intolerance,’’ one for every shot, to secure the film’s copyright.

But Griffith, an obsessive editor, continued to alter “Intolerance’’ between that deposit and the premiere, and for years afterward. He excised the Babylonian and modern sequences, turning them into stand-alone features. He reassembled the film, making adjustments throughout the 1920s. And, at multiple steps along the way — the European premiere, the spinoffs — Griffith commissioned new scores, from new composers.

A 1989 attempt by the Museum of Modern Art and the Library of Congress to reconstruct the 1916 version of “Intolerance’’ based on the copyright deposits pointed up, as musicologist Julie Brown has noted, the danger of such reconstructions, with their “many compromises and educated guesses,’’ being taken as definitive. Was fitting the footage to Breil’s often-sketchy score creative inference, or the tail wagging the dog? Should presentations re-create the premiere’s historical moment or respect Griffith’s later, presumably final judgment? Subsequent restorations of “Intolerance’’ opted for all-new scores from latter-day composers: modern intrusion or a nod to Griffith’s pragmatic spirit?

Breil himself aspired to classical-canon permanence, but his one-act opera “The Legend’’ — premiered, on an all-American triple bill, at the Metropolitan Opera — was scuttled by savage reviews. In 1924, he suffered a breakdown while working on Griffith’s Revolutionary War picture “America.’’ The subsequent effort of mounting another one-act opera, “Der Asra,’’ hastened his decline. Two months after the performance, at the age of 55, he died.

Matthew Guerrieri

Matthew Guerrieri can be reached at matthewguerrieri@gmail.com.