Iax

Iax is an agri-world of Ultramar whose fertility once rivalled Macragge and Konor, until Mortarion’s Plague Wars reduced it to a death world. Sited within the Ultramar sector of the Imperium of Man, it fell during the Nurgle offensives that followed the opening of the Great Rift, and its ruin stands as one of the defining losses of that campaign.

Before its fall, Iax was administered as one of Ultramar’s garden worlds, its climate and soil given over almost entirely to grain and orchard cultivation in support of the Five Hundred Worlds. Its produce fed populations across the sector, and by the close of the Great Crusade its standing among Ultramar’s agricultural planets was matched only by Macragge itself and by Konor. Generations of Ultramarines administration maintained that productivity largely undisturbed, and Iax entered the late 41st millennium as a settled, unremarkable asset of the Imperium Sanctus.

That security ended with the Plague Wars, the campaign by which the Death Guard Primarch Mortarion sought to break Ultramar following the opening of the Great Rift. Daemonic legions serving Ku’gath Plaguefather, a Great Unclean One raised high in Nurgle’s following, descended upon Iax’s farmland, corrupting soil and crop alike. Roboute Guilliman, Primarch of the Ultramarines and regent of the Imperium, met Mortarion in single combat on the planet’s surface, a duel recorded among the notable engagements between the two brothers since the Horus Heresy.

Guilliman prevailed, driving Mortarion from the field, but the victory could not restore what the invasion had ruined. Imperial forces subsequently burned the surviving farmland to arrest the spread of Nurgle’s corruption, and Iax was reclassified a death world in the campaign’s aftermath. Guilliman himself has judged that the taint may not lift for centuries, if ever, leaving the planet’s recovery uncertain and its former role in Ultramar’s agriculture unfilled.

Iax remains, in the current era, a marker of the Plague Wars’ cost to Ultramar, cited alongside Macragge and Konor whenever the sector’s garden worlds and their fates are discussed. Its history binds it into the wider account of the Indomitus Crusade and of Guilliman’s continuing conflict with Mortarion, and it stands as a fixed point where the Ultramarines’ home sector and the Death Guard’s war against it intersect.