“ ‘Metropolis’ is the most iconic silent picture of its day, mainly because of the visual ambition and virtuosity of the film itself,” said Noah Isenberg, editor of “Weimar Cinema,” a book about early German films, and a professor of film and literary studies at the New School. “But until now, we didn’t have the full story. These additions are really essential to understanding the full arc of the narrative.”

Image A scene from the newly recovered footage of Fritz Lang's 1927 “Metropolis.” Credit... Kino International

Made at a time of hyperinflation in Germany, “Metropolis” offered a grandiose version  of a father and son fighting for the soul of a futuristic city  that nearly bankrupted the studio that commissioned it, UFA. After lukewarm reviews and initial box office results in Europe, Paramount Pictures, the American partner brought in toward the end of the shoot, took control of the film and made drastic excisions, arguing that Lang’s cut was too complicated and unwieldy for American audiences to understand.

Mr. Peña discovered a full-length copy of “Metropolis” in 2008 in the archives of the Museo del Cine in Buenos Aires. He had first heard stories 20 years earlier that a two-and-a-half-hour print had somehow found its way to Argentina and was wandering from one government institution to another, but his efforts to gain access to the film cans had always been frustrated by an indifferent bureaucracy.

Since the 1930s, the full-length version of “Metropolis” had been part of a large private archive assembled by a prominent Argentine film critic, Manuel Peña Rodríguez, who would lend titles to local film clubs. At his death around 1970, the collection was donated to the Argentine version of the National Endowment of the Arts, which handed it off to the Museo del Cine in 1992.

Over the years, Mr. Peña had shared his frustrations at not being given access to the film with Paula Félix-Didier, another film archivist and, during the 1990s, his wife. When she became head of the Museo del Cine in 2008, she said, “I called Fernando and said, ‘Just come, let’s do it.’ So he came, we looked for the cans, and there they were, cataloged and up on a shelf.”