Inwit is an Imperial Ice World located in the Inwit Cluster of the Segmentum Solar. It is known that Rogal Dorn, the Primarch of the Imperial Fists Legion, spent a significant portion of his life on Inwit before he was rediscovered by his father the Emperor of Mankind and joined the forces of the Imperium of Man during the Great Crusade in the late 30th Millennium. Dorn lived amongst the ice-tribes who called Inwit home and considered one of the chieftains of these tribes to be his adoptive grandfather and chief childhood mentor. The world's population was said to inhabit massive ice-hives and its actual level of technological advancement remains unclear. The people of Inwit were known to have divided themselves into different tribes and clans and to have a caste system in place known as ice-castes. Dorn claimed to have risen to have become the emperor and warlord of Inwit and its entire star system and to have either discovered or constructed the massive starship later used as a mobile fortress-monastery by the Imperial Fists known as the Phalanx. Inwit at present is one of only two known primary recruiting worlds for the Imperial Fists Chapter of Space Marines, along with the Hive World of Necromunda. Very little is known about this world in current Imperial records.
Inwit was, and is, a world of death and cold. Its star is old and withered, bleeding the last of its heat as cold, red light. Tidally locked against its dying star, perpetual darkness soaks one side of the planet, faded sunlight the other. Crevasse mazes, frozen mountain ranges and plains of frost dunes cover the planet's dark side -- this is the Splintered Land, the beast-stalked wilderness which shapes the bodies and beliefs of the human population that clings to life here. Under the ice crust, thick seas flow in sluggish tides and pale and sightless creatures swim the waters, hunting by vibration and a preternatural taste for blood. Far above this desolation, great and ancient space stations and shipyards look down on the cold-shrouded worlds through perpetual auroras -- created in a lost past, these citadels of the void have looked down on Inwit since before any records or tales can recall. Whilst on the planet, the light side of Inwit offers little more comfort than the dark, being a land of drift-crusted saline seas and sparse bare rock under the unblinking gaze of the red sun.
There is little of value on Inwit; its seas are buried or lifeless, its mountain bare of riches and its native species vicious. There is, however, one thing that this harsh world produces that led it to conquer a star cluster and endure as an island empire of order in the Age of Strife: its people. Though they are barbaric, they are far from unsophisticated. The warriors of Inwit are raised to endure and survive. The world that bears them teaches them to never relent and that the price of weakness is death, for them and the rest of their kin. Death comes in many forms on Inwit; in the ice storms that can freeze and cover a man in seconds, at the claws of the predators that roam the Splintered Lands, and in the lapse in concentration that allows the cold to penetrate the warmth-seals of a hold. These factors make a certain kind of people: strong, grim and dedicated to the survival of the whole rather than the individual. Much of the world's population is nomadic, moving between the subterranean ice hives to trade in weapons, fuel and technology. Conflict between the roaming clans is common and young warriors learn how to defend against their clan's enemies as early as they learn how to endure the death touch of Inwit's merciless chill. They know how to learn, have an innate sense of an object's functional value and, most importantly, they have the strength to conquer those who possess knowledge they do not.
Long ago, before the coming of the Emperor was even a dream on night-shrouded Terra, the people of Inwit began to create their own realm in the stars. On every world they took, they assimilated, realigned and reinforced. With each conquest their culture and learning grew, but Inwit itself remained unchanged even as it became the centre of a stellar empire. The ice hives and clan disputes remained and while their world birthed starships and ringed its orbits with weapon stations, its rulers kept to the old ways, the ways that had created their strength, the warlords and matriarchs who commanded armies amongst the stars still living lives little easier than their vassals. So it was, and so it is now.
It was as part of this burgeoning empire that Rogal Dorn grew to manhood, and then to rule its domains as emperor. Much of his early years remains unknown, or at least little talked about. What is known is that from the cold and darkness of Inwit the boy, named Rogal by his adoped kin, rose to lead the House of Dorn or the Ice Caste and then to the rule of the Inwit Cluster. The patriarch of the clan that raised Dorn became an adoptive grandfather to him, and taught him much of tactics, strategy, and diplomacy. Even after he discovered he was not blood-related to his "grandfather," Dorn held his memory in high value; he kept a fur-edged robe that had belonged to the man and slept with it on his bed every night. His qualities married perfectly with those of Inwit, and he pushed their empire further than any other, ordered and trained its armies, and fashioned spacecraft the like of which had not been seen before. When the true Emperor was reunited with Rogal Dorn, He regained not only a lost son, but the strength of a star-spanning society already forged into a tool of war.
- The Horus Heresy - Book One: Betrayal (Imperial Armour), pp. 290-291
- The Horus Heresy - Book Three: Extermination (Imperial Armour), pp. 58-60
- Space Marine (Novel) by Ian Watson (no longer considered canon)
- Horus Heresy Chapbook (Anthology), "The Lightning Tower" by Dan Abnett, pp. 5-6