The word "Tartarus" is a term from Greek religion that refers to the place where evil spirits and wicked men who have died are punished. Alternate translation: "he cast them into hell" (See: [[rc://en/ta/man/jit/translate-names]])
This can be stated in active form. Alternate translation: "where he will keep them in chains of lower darkness" (See: [[rc://en/ta/man/jit/figs-activepassive]])
Possible meanings are 1) "in chains in a very dark place" or 2) "in very deep darkness that imprisons them like chains." (See: [[rc://en/ta/man/jit/figs-metaphor]])