Iax, once known as the "Garden of Ultramar," is a Dead World that was once an Imperial Agri-world and a part of the Realm of Ultramar that is ruled by the Ultramarines Space Marine Chapter and lies in the Ultima Segmentum.
Iax's climate and fertility once made it one of the most naturally agriculturally productive worlds in the Imperium. The inhabitants harnessed the planet's inherent fertility, covering its surface with well-ordered farms and cultivated woodlands. There were no large cities on Iax, but many small towns dotyed the landscape, connected by an efficient system of fast hydroways. The oldest and most densely urbanised area of Iax was the ancient fortress city of First Landing, whose tall citadel withstood the barrage of many invaders over the long centuries.
However, during the Plague Wars of the early 42nd Millennium, the Realm of Ultramar, under assault by the forces of the Plague God Nurgle, was suffering disease and combat-related casualties at a terrifying rate. As a result, following the end of the Indomitus Crusade and his return to Ultramar in 111.M42 to aid its defence, Lord Commander of the Imperium Roboute Guilliman redesignated Iax to serve as a "Hospital World" for the duration of the conflict.
In the final battle of the conflict, the Daemon Primarch Mortarion and his forces retreated off-world and left Ultramar behind, but not before detonating a Virus Bomb that scoured all life from once-verdant Iax.
At the time of the Horus Heresy in the early 31st Millennium, Iax was one of the four Master Worlds of Ultramar. These worlds were the seats of government of the four major fiefdoms of the Five Hundred Worlds, ruled over by an official known as a Tetrarch. These "Princes of Ultramar" were highly distinguished Veterans of the Ultramarines Legion, second only to the mighty Guilliman himself and providing him with a chosen champion and an Honour Guard. The Tetrarch of Iax at the time of the Heresy was Stolos Amyntas.
The Plague Wars
After Guilliman's resurrection in 999.M41 during the Ultramar Campaign and restoration as the Lord Commander of the Imperium, he embarked on the Indomitus Crusade to reclaim the worlds of the Imperium. However, the followers of the Plague God Nurgle had assailed the worlds of the Ultramarines in the Realm of Ultramar, and the infernal diseases of the Archenemy claimed far more lives than their weapons. Still engaged in the Indomitus Crusade far from his homeworld, Guilliman redesignated Iax as a "Hospital World" for the duration of the conflict.
Landing the sick and wounded at Iax's Hortusia spaceport took an amount of time congruous to the complexity of the task. The diseases spread by the Plague God's servants were supernaturally potent, so quarantine procedures had to be stringent. Like everything in Ultramar, if a job were deemed of enough importance to be done, then it was to be done correctly. As new patients were brought down by shuttle, decontamination crews waited on the landing field and its surrounding mushroom patch of white dome tents. Between each trip, the shuttles were vigorously decontaminated on the ward-ships in orbit, for that was the responsibility of their medicae-captains, but ensuring the purity of the landing fields fell to the Chirurgeon-General's Office on Iax. Adeptus Mechanicus biologians attached to the Officio Medicae on Iax calculated atmospheric reentry patterns to burn the worst of any contamination remaining on the spacecrafts' hulls away.
Upon Iax, the lesser sick recuperated alongside the injured. Some of the diseases unleashed on Ultramar could be treated under median-range quarantine conditions with standard medicines. Others required specialist care, up to and including Adeptus Ministorum-approved exorcism. Those suffering from the more aggressive, spiritually corrupting daemonic illnesses were held on specially-commissioned void stations in orbit. As few as possible were euthanised. Around Iax, troops exhibiting symptoms were divided by type according to standard triage protocols. Those who had died en route were easiest to separate. After the dead, the first appraised were those suffering purely from injury, be it physical or mental. They were also rigorously tested for disease. Those who proved free of secondary infections were separated from the rest and taken to the surface via decontamination protocols at Star Fort Korsteel, which had taken up anchor over Iax for the purpose. The remainder of the casualties judged to be suffering from an illness -- whether physical or not -- were returned to the main group.
The sick were split into known and unknown pathogen groups, then further into physical, mental and spiritual afflictions, then by grade of severity, and finally all these groups were divided between the wounded sick and the merely sick. After all this, the groups were further subdivided into numbered cohorts and relocated to holding vessels in permanent orbit. There, another round of anti-biological procedures were undertaken. Second and third rounds of testing virtually eliminated any possibility of transmission. Those that passed the third test were deemed safe and transferred to the surface of Iax, bound for facilities that treated all ailments.
Yet Iax was not spared from the full brutality of the Plague Wars. In 111.M42, the Great Unclean One Ku'Gath the Plaguefather launched an invasion of Iax at the head of seven daemonic Plague Legions under his command. The existence of Iax as a Hospital World had greatly offended the Plague God, for it worked to disrupt his "gifts" to Mankind and his plans to add the Realm of Ultramar to his own domain. Despite all the desperate precautions undertaken to prevent the spread of plague, seven soldiers were marked by Nurgle through various means, ranging from obvious trauma to minor scratches, unnoticed wounds and even fly bites.
One evening, these seven infected were drawn unknowingly to a secluded lake where they went through horrifying transformations, some of them fully aware, as insects and maggots burst through their mutating and rotting bodies as they died. These ritualistic deaths opened a rift into the Garden of Nurgle in the Warp. Through the portal came seven mighty plague arks, created from the carcasses of Void Whales surrounded by billions of flies carrying various diseases. It seemed the inevitable doom of Iax had finally come.
But salvation was already at hand. For with the end of the Indomitus Crusade following the Battle of Raukos, Roboute Guilliman and his forces had returned to Ultramar to lead its defence and aid its beleaguered defenders. Guilliman concentrated upon defeating the forces of the Death Guard Traitor Legion led by his brother, the Daemon Primarch Mortarion, who had joined Ku'Gath upon Iax after his invasion force had been repulsed at both Espandor and Parmenio. Guilliman followed Mortarion to Iax and the two engaged in a great duel there that marked the climax of the Plague Wars. The two Primarchs fought to a stalemate once more, and then Mortarion and the Death Guard retreated following the use of a Virus Bomb. The Plague Wars of Ultramar ended shortly thereafter, when the forces of the other Chaos Gods invaded the Scourge Stars as part of the Great Game and Nurgle was forced to withdraw his own forces from Ultramar in order to defend his new domain.
- Codex: Ultramarines (2nd Edition), pp. 14-15
- The Horus Heresy - Book Five: Tempest (Forge World Series) by Alan Bligh pg. 81
- Warhammer 40,000: Rulebook (8th Edition), pp. 53, 158, 167
- Know no Fear (Novel) by Dan Abnett
- Dark Imperium (Novel) by Guy Haley, Chs. 5, 14, 16
- Regimental Standard - Five Wonders of Ultramar