The Iron Collar is the portion of the Jericho Reach in the Segmentum Ultima under the control of the Imperium of Man that includes a wide arc of Imperial listening posts, void defence stations and Fortress Worlds spread out across the portion of the Reach bordering the Well of Night.
The worlds and outposts of the Iron Collar provide the primary base for Imperial operations in the region and represents the headquarters from which the three salients of the ongoing Achilus Crusade are supported.
Among the fortified worlds within the Iron Collar, Karlack serves as the keystone and de facto Imperial capital of the region. The Iron Collar also includes the Fortress Worlds of Calisi, Alphos, Hethgard, Pyrathas and Spite.
- Deathwatch: Core Rulebook (RPG), pg. 345
- Deathwatch: The Achilus Assault (RPG), pg. 16