Mercury
Mercury is one of the inhabited worlds of the Solar System.
Darrow has captured Mercury for the Republic before returning to Luna at the opening of Iron Gold. His decision to launch the Iron Rain against the Senate's wishes contributes to the political crisis.
The Free Legions fight Atalantia's forces on Mercury. Orion's use of the Storm Gods causes catastrophic flooding, and Lysander's uprising in Heliopolis helps bring about the Republic's defeat.