The enormous success of Disney’s Frozen — the top-grossing animated film of all time — is also a testament to the value of perseverance. Walt Disney himself first examined the possibility of bringing Hans Christian Andersen’s The Snow Queen to the screen in animated form as far back as 1937, and his studio made multiple attempts to make a movie version, decades before Frozen finally succeeded in 2013.

But Frozen is just the most obvious example. For every animated movie Disney has produced over the studio’s 80-year history, it seems like there were another two or three that got lost along the way. Below you’ll find eight unmade projects from the Disney vaults. Could there be another Frozen-style billion-dollar blockbuster among them? Read on and see.

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Chanticleer

(1938-1960)

After the success of his first full-length animated feature, Snow White and the Seven Dwarves, in 1937, Disney came across Chantecler, a well-loved stage play by Cyrano de Bergerac author Edmond Rostand, based on a classic European fable about a self-regarding rooster who believes that his crowing makes the sun to rise. An adaptation went into development, but the animators found it difficult to make the title character sympathetic. Another French folk character, Reynard the Fox, was introduced as a villain (and the spelling was altered to Chanticleer), but the story didn’t come together. With the advent of World War II, the project was scrapped, though there were several failed attempts to revive it in the late 1940s. It was brought back again in the early 1960s, when animators Ken Anderson and Marc Davis found the old concept art and attempted to retool the story as a Broadway-style musical comedy. But with Disney focused on the construction of what would become Walt Disney World in Florida, the decision was made to scale back on animation production, and the studio moved forward with The Sword in the Stone instead. (Animator Don Bluth eventually made a poorly received version of the story outside Disney,1992’s Rock-a-Doodle.)

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Don Quixote

(1940-present)

It’s probably appropriate that Cervantes’s classic tale of a deluded hero on a hopeless quest has thwarted so many filmmakers over the years. Director Terry Gilliam famously has been on a 15-year quest to film the story of an elderly man who believes he’s a knight fighting giants (actually windmills). But that’s nothing compared to the 75-year saga of Disney’s attempt to make an animated feature out of it. Work initially began in 1940, but despite some lovely Velásquez-inspired artwork, the film was scuppered by the war and the poor box office of Pinocchio and Fantasia. A second version, based on Richard Strauss’s music, was begun in 1946 but didn’t get very far. A third was started in 1951, but no one could figure out how to slim down Cervantes’s epic or make its unhinged hero sympathetic. The project spent a few decades dormant, but in the late 1990s, French animators Paul and Gaëtan Brizzi began working on a new version, which got close to going into production but was eventually deemed too dark and adult for the studio. We could yet see a Disney Don Quixote though: The studio has been developing a live-action version with Johnny Depp since 2012.