Thirteen Ghosts, the 2001 remake of William Castle's 1960 film, packs a lot of big ideas into its 90-minute runtime, not the least of which is the "Black Zodiac," which provides the origin of its titular ghosts.
In the 1960 original, 13 Ghosts, Dr. Plato Zorba perishes and leaves a large house to his struggling nephew, Cyrus. Unfortunately for Cyrus and his family, the house also contains the uncle's collection of a dozen ghosts - including a lion tamer and his lion, an Italian chef, a flaming skeleton, and others - all waiting for the arrival of a 13th ghost that will free them. The film's claim to fame was its use of colored filters to make the ghosts "invisible" unless viewed through special "ghost viewers" that were handed out to members of the audience.
The remake follows the same basic plot - an eccentric uncle wills a house full of ghosts that can only be seen through special glasses to his nephew's impoverished family - but with an entirely new roster of ghosts. Their presence is also much more integral to the plot. Whereas the ghosts in the original are mostly a MacGuffin (the plot actually revolves around a human villain looking for a fortune hidden in the house), the ghosts in the 2001 version are what powers the uncle's infernal machine.
Thirteen Ghosts also features a character named Cyrus (played by F. Murray Abraham), but this time he's the sinister uncle and his bizarre house is actually a gateway to hell. "Designed by the devil and powered by the dead," Basileus's Machine is said to have been conceived by a 15th-century astrologer while he was possessed by a demon. The plans for the machine are in a book called The Arcanum, which also describes the ghosts needed to power it. The house itself is an enormous ghost trap, complete with transparent walls etched with spells and made of "ectobar glass." (Behind the scenes, the set was designed and fabricated by production designer Sean Hargreaves, who has also worked as an illustrator on many of the movies in the Marvel Cinematic Universe.)
Why does Cyrus want to crank up this machine? Apparently, because it's the only way to gain access to the Ocularis Infernum, an "eye in hell that sees everything," including the past and the future. "If knowledge is power, then the man who controls the Ocularis would be the most powerful man on Earth," Cyrus says.
According to The Arcanum, there are 13 ghosts necessary to access the Ocularis Infernum: 12 needed to power it, and a 13th to shut it down if necessary (though that last part proves to be a lie). These ghosts align with the "Black Zodiac," which was created for the movie. (Though that doesn't mean the film doesn't have significance along traditional zodiac lines.) Besides maybe the elaborate puzzle box of the house itself, these ghosts are the most memorable part of this oddball film. They are brought to (un)life thanks to the special effects work of Robert Kurtzman and Greg Nicotero, and each one matches one of the entries in this mythical "Black Zodiac."