Broad expanse of space with a very low density of stars lying spinward of the main region of
the Third Imperium. The Great
Rift is a pronounced
impediment to interstellar travel, and it constrains jumps through Corridor sector to the Spinward Marches.
The Great Rift is one of many astrographic terrain features which have
long-term security for the Third Imperium. By its very nature, the
Rift has made outside incursions difficult, which has made the interior
the Imperium a secure population center.