Delphic Expanse

The Delphic Expanse was an area of space approximately 50 light years away from Earth. It was 2,000 light years across, according to the Vulcan Ambassador Soval. The Expanse was riddled with a web of dangerous spatial anomalies and was surrounded by a dense layer of thermobaric clouds, which made navigation to starships extremely hazardous. Being artificially created by transdimensional beings using a vast number of massive spheres, the Delphic Expanse ceased to exist in 2154, when the Earth starship destroyed them. 

History
In 2133, a Klingon starship attempted to enter the Delphic Expanse. When it reemerged, the entire crew was anatomically inverted but still alive. After this incident the Klingons would not enter the Expanse. Vulcan ships had also entered the Expanse, but only a few had ever returned. 

In December 2152, the Vulcan ship Seleya embarked on a mission to chart the thermobaric clouds surrounding the Expanse. After several days the ship's crew reported that the Seleya was caught in a subspace eddy and being pulled into the Expanse and contact was lost. The crew of the Vulcan ship Vaankara, sent to search for the lost Seleya, went insane, killing each other and self-destructing the ship after only two days inside the Expanse. After this the Vulcans considered any expedition into the Expanse to be a foolishly risky action. The Enterprise would later find the Seleya adrift, with its crew gone insane due to trellium-D exposure. 

When Earth suffered a devastating attack which resulted in the deaths of seven million people in March 2153, Captain Jonathan Archer received intelligence from the Suliban Cabal's mysterious benefactor that the attack had been launched by the Xindi, a race native to the Expanse. With this information, the Enterprise embarked on a mission into the Expanse to find the Xindi, in an attempt to prevent another attack which would destroy Earth. 

While in the Expanse, Enterprise encountered the Triannons, a native species which regarded the Expanse as the "Chosen Realm," an area that had been created by supernatural beings they referred to as "the Makers," in preparation for their eventual return. As they spent more time in the Expanse, the Enterprise crew discovered that the Triannon myth was based in fact, and that the Expanse had been created by a race of transdimensional beings who were attempting to reconfigure space to make it habitable for their species as a prelude to invasion. 

The crew discovered that this race had constructed a series of massive spheres, each one of which emitted powerful waves of gravimetric energy, which were responsible for the spatial anomalies. Posessing advanced temporal technology which allowed them to examine alternate timelines, the Sphere Builders discovered that, in the 26th century, the Federation was destined to finally defeat the Sphere Builders and drive them back into their transdimensional realm. In an attempt to prevent this future, the Builders contacted the Xindi and led them to believe that humanity would eventually be responsible for the destruction of their homeworld, and that the only way to save themselves was to destroy Earth first. 

In early 2154, Captain Archer was eventually able to convince the Xindi that they had been manipulated, and entered into an alliance against the Sphere Builders. Enterprise was successful in disabling one of the Spheres with a deflector pulse, causing a chain reaction which destroyed the entire Sphere network. This effectively caused the Expanse to cease to exist, and the thermobaric cloud perimeter dissipated. 

Astronomical objects

 * Arakon system
 * Azati Prime system
 * Calindra system
 * Muratas Cluster
 * Orassin distortion field

Sentient species

 * Haradin
 * Ikaarans
 * Illyrians
 * Kovaalans
 * Loque'eque
 * Skagarans
 * Tarquin's species
 * Tret's species
 * Triannons
 * U'tani
 * V'radians
 * Xindi

Background
The size, mentioned by Soval, presumably did not refer to a spherical diameter of the expanse, as such a huge phenomenon would be a dominant feature within the galaxy. If the size is accurate, it would suggest the expanse was a somewhat flat region of space.

Apocrypha
The Pocket ENT novel Rosetta establishes the technical scientific name of the Expanse as "the D-4853 anomaly."

Delphische Ausdehnung Expansión Délfica Etendue Delphique Distesa Delfica Delphic Expanse Дельфийское пространство