The Ring of Iron is the name given to the massive complex of orbital shipyards, refineries and construction facilities that encircle the equator of the Adeptus Mechanicus' homeworld of Mars in the Sol System.
During the Horus Heresy in the Schism of Mars, the Dark Mechanicum struck against the Ring of Iron and damaged large portions of its facilities. The terrible destruction could be seen from the surface of Mars as a blazing fire in the sky.
After the end of the Heresy and the reestablishment of Imperial rule over Mars, the Ring of Iron was repaired and put to work once more churning out the starships of the newborn Imperial Navy and the Imperial merchant fleets.
In the late 41st Millennium, spacecraft and other large starfaring structures are constructed within the Ring's extensive orbital factories, and many of the warships of the Battlefleet Solar are based in its huge floating docks. It is considered the largest known man-made structure in the Milky Way Galaxy.
- Codex: Adeptus Mechanicus - Cult Mechanicus (7th Edition), pg. 21
- Mechanicum (Novel) by Graham McNeill