Slipspace portals are a method of slipstream space transit developed by the Forerunners. Essentially a large-scale application of slipspace translocation, slipspace portals are designed to transport enormous amounts of mass between two fixed points on a continuing basis.
Large constructs, such as the Halo installations, could be transported across interstellar distances through the use of portals. The transition of such a large object would slow down other slipspace traffic in the entire galaxy. While designed for large-scale transit, portals have a limited transit capacity and can be strained or even destroyed if this capacity is exceeded. Portals also have a system that filters unnecessary objects such as debris, discarding them into the volume of slipspace. While passage through a portal is remarkably faster than an ordinary slipspace jump, portal transit is not instantaneous; for example, the passage from the Earth portal to the Ark took over three weeks.
Portals may be generated by groundside facilities which vary in overall architecture but are typically enormous, or generator systems situated in space. Portals generated within an atmosphere are often accompanied by severe weather disturbances.
Portals are similar in appearance to a slipspace rupture generated by a slipspace drive, appearing as holes into the pitch-black void of slipspace and surrounded by blue-violet energy and supported by a web of hard light. Some portals, however, allow visibility to the destination on the other side.
The Forerunners had a network of portals that allowed fast passage throughout their ecumene. Some systems, including that of the capital, had portal installations that connected to multiple worlds. The Librarian used an array of portals to travel to the worlds where she collected the various species of the galaxy for indexing at the Ark. The same network was used to transport the Halo rings. The portals in this network could only be activated by a special type of vessel, known as a keyship, most of which were eventually destroyed by the Librarian in order to prevent the Flood from reaching the Ark. The generator device for one of the Librarian's portals was buried near the town of Voi on Earth, and was later activated by the Covenant, who were in possession of the last known remaining keyship, known as the Forerunner Dreadnought.
The Halo: Reach multiplayer map High Noon is set in an observation platform of a portal generator. This portal facility is noticeably different from the Earth portal; in addition to a different structural design, the area of space beyond the portal is visible, as opposed to complete blackness. This particular portal device also generates a storm of swirling debris in the immediate area around the portal, just beyond the map's borders.
 List of appearances
- Halo 3 (First appearance)
- Halo Legends
- Halo: Reach
- Halo: Cryptum
- Halo: Combat Evolved Anniversary
- ^ Halo: Cryptum, page 200
- ^ Halo: Cryptum, page 274
- ^ Halo: Cryptum, page 104
- ^ Halo: Cryptum, pages 313-314
- ^ Halo: Cryptum, page 323
- ^ Halo Waypoint, Hero-Fortitude
- ^ a b c Halo: Combat Evolved Anniversary, multiplayer map High Noon
- ^ a b c Halo: Cryptum, page 312
- ^ a b c Halo 3, campaign levels, The Storm and Floodgate
- ^ Halo: Combat Evolved Anniversary, Terminal 2
- ^ Halo: Cryptum, page 310
- ^ Halo Waypoint: The Halo Bulletin: 11/9/11
- ^ Halo 3, Terminal 4
- ^ Halo Waypoint: The Halo Bulletin: 10/19/11