The Macragge System is an Imperial star system located in the Realm of Ultramar in the Segmentum Ultima. It is the home system of Macragge, the Civilised World that is both the capital world of the Ultramar Sub-sector and the Chapter homeworld of the Ultramarines Chapter.
The worlds of the Macragge System, from closest to the system primary to farthest, include:
- Nova Thulium - Nova Thulium is the innermost and first world of the Macragge System and an Agri-world that was one of the many planets invaded by the Chaos forces of Abaddon the Despoiler during the Ultramar Campaign of the 13th Black Crusade in 999.M41.
- Ardium - Ardium is the second world of the Macragge System and a Hive World that was one of the many planets invaded by the Chaos forces during the Ultramar Campaign. During this assault, a warband of the Iron Warriors Traitor Legion, the Bitter Sons, captured one of Ardium's three subterranean hive cities -- Hive Magmaria -- but the resurrected Primarch Roboute Guilliman later led the Ultramarines' 4th and 6th Companies to free the world and eliminate the Bitter Sons. Ardium was once more the site of fighting between the Ultramarines and the Forces of Chaos, this time in service to the Plague God Nurgle, during the Plague Wars. Ardium had three major hive cities, including Hives Geodrane, Magmaria and Tarnas, all of which were built down into the world's crust rather than above the surface. The planet is famed for its large-scale bio-habitats.
- Thulium - Thulium is the third world of the Macragge System and a Death World. It, too, was one of the worlds that saw fighting between the Ultramarines and the forces of the Despoiler during the Ultramar Campaign.
- Laphis - Laphis is the fourth world of the Macragge System and a Shrine World of the Adeptus Ministorum. During the Ultramar Campaign of the 13th Black Crusade, it came under the control of the forces of the Alpha Legion before they were routed from the world by a counterinvasion led by Chapter Master Marneus Calgar of the Ultramarines. Laphis has three moons -- Halo, Aurora, and Nimbus.
- Macragge - Macragge is the fifth world of the Macragge System, the eponymous planet of the system, a Civilised World and the homeworld of the Ultramarines and Roboute Guilliman, as well as the capital world of the sub-sector.
- Mortendar - Mortendar is the sixth and outermost planet of the Macragge System and a Fortress World of the Imperium. Like the rest of the system, it fell under assault by the servants of Chaos under the command of the Despoiler during the Ultramar Campaign.
- Gathering Storm - Part Three - Rise of the Primarch (7th Edition), pp. 11, 41-47