The Hades Gulf, or Orion-Eridanus Gulf, is a several-hundred-light-year buffer zone of mostly uninhabited space between the human and ex-Covenant spheres. The Gulf's status as a key crossing region was first discovered during the second half of the Human-Covenant War through observation of the Covenant's invasion pattern, with the UNSC identifying the Covenant invasion channel in the region as the Pleiades Corridor due to its proximity to the Pleiades star cluster. At the time, it was flagged as one of two primary viable avenues for retaliatory strikes into Covenant territory (i.e. ones that did not rely on Covenant slipspace transit). In the post-war era, it has rapidly become a strategic and economic hotspot as various actors from both sides of the Gulf have claimed worlds along its length, largely building upon infrastructure originally established by the Covenant for their invasion fleets.