The Black Zodiac is a zodiac consisting of thirteen earth-bound spirits which will activate Basileus's Machine and open the Ocularis Infernum.
The order in which the ghosts are placed on the zodiac seems to be based on how dangerous they are (with the exception of The First Born Son, who is threatening regardless of being the first ghost, while the next three seem benign, or at least unable to do damage).
Ghosts
There are thirteen souls bound to earth, foretold and described in The Arcanum, which make up the Black Zodiac, as follows:
The First Born Son
The first ghost in the Black Zodiac. The First Born Son is the ghost of a little boy who dies of a shot through the head. Cyrus chose the ghost of Billy Michaels as the First Born Son.
The Torso
The second ghost in the Black Zodiac. The Torso is missing his legs, and/or his waist. Cyrus chose the ghost of Jimmy Gambino as the Torso.
The Bound Woman
The third ghost in the Black Zodiac. This ghost is of a woman who died having been tied-up in some fashion. Cyrus chose the ghost of Susan LeGrow as the Bound Woman.
The Withered Lover
The fourth ghost in the Black Zodiac. This ghost is of someone who died having a withered or worn appearance. Cyrus chose the ghost of his niece-in-law, Jean Kriticos, as the Withered Lover.
The Torn Prince
The fifth ghost in the Black Zodiac. This ghost has much of the skin on the right side of his body missing, leaving the bones and muscles. Cyrus chose the ghost of Royce Clayton as the Torn Prince.
The Angry Princess
The sixth ghost in the Black Zodiac. This ghost apparently is of a young woman who dies by committing suicide. Cyrus chose the ghost of Dana Newman as the Angry Princess.
The Pilgrimess
The seventh ghost in the Black Zodiac. Cyrus chose the ghost of Isabella Smith as the Pilgrimess.
The Great Child and The Dire Mother
The eighth and ninth ghosts in the Black Zodiac. The Great Child is the ghost of a very large and overweight child, and the Dire Mother is that of a very small stature. Cyrus chose the ghosts of Harold and Margaret Shelburne as the Great Child and the Dire Mother.
The Hammer
The tenth ghost in the Black Zodiac. This ghost is that of a muscular, heavy-set blacksmith who wields a large hammer. Cyrus chose the ghost of George Markley as the Hammer.
The Jackal
The eleventh ghost in the Black Zodiac. The Jackal is the ghost of a dishevelled man wearing a cage on his head. Cyrus chose the ghost of Ryan Kuhn as the Jackal.
The Juggernaut
The twelfth ghost in the Black Zodiac. This ghost is that of a tall, ugly and incredibly strong man. Cyrus chose the ghost of Horace Mahoney as the Juggernaut.
The Broken Heart
The thirteenth and final ghost in the Black Zodiac. This ghost dies by leaping into the core of Basileus's Machine out of an act of pure love. Cyrus chose his nephew, Arthur Kriticos as the Broken Heart.