Iax, known as the "Garden of Ultramar," is an Imperial Agri-World and is a part of the Realm of Ultramar that is ruled by the Ultramarines Space Marine Chapter and lies in the Ultima Segmentum. It is one of the most productive worlds within the Imperium of Man.
Iax is an Agri-World whose climate and fertility have made it one of the most naturally productive worlds in the Imperium. The inhabitants have harnessed the planet's inherent productivity, covering its surface with well-ordered farms and cultivated woodlands. There are no large cities on Iax, but many small towns dotted over the landscape, connected together by an efficient system of fast hydroways. The oldest and most densely urbanised area of Iax is the ancient fortress city of First Landing, whose tall citadel has withstood the barrage of invaders over the centuries.
- Codex: Ultramarines (2nd Edition), pp. 14-15