The Kelsac Periphery is the galactic coreward-southern border region of the Siakar Expanse, bordering the Hades Gulf. It is a hazily-defined area of space where, over a roughly 200-300-light-year span, what the Covenant consider "civilized" worlds gradually thin out and uncharted space begins. During the Covenant's reign, many fringe elements such as pirates and anti-centralization dissidents called the area home; there were parts of the vast Covenant frontier where rogue worlds, systems or even entire interstellar groupings existed for decades or centuries effectively outside High Council authority, only to be re-assimilated as the Covenant's slow but inexorable expansion front reached them. Indeed, a notable number of the conflicts the Covenant experienced were focused on the re-integration of break-off elements such as these. During the Human-Covenant War, the Covenant took significant steps to pacify the immediate region surrounding the sliplanes their expeditionary fleets used to assault the human sphere. Since the Covenant lacked formal maps of their far-flung frontiers for the most part, it is likely that there are dozens or more sites of activity in the Hades Gulf unknown to both the Concord of Reconciliation and the UNSC.