"Why would someone want to create a web of crippling anomalies?"
The Delphic Expanse spheres were a series of artificially-created objects that were scattered around the Delphic Expanse. The spheres, each one nineteen kilometers in diameter, generated massive amounts of gravimetric energy and were collectively responsible for the web of spatial anomalies which constituted the Expanse. Each sphere was surrounded by a cloaking barrier which kept it hidden from outside observers. According to the Xindi-Primate Degra, the Xindi knew of seventy-eight spheres, at last count. (ENT: "The Forgotten")
Starfleet first encountered the spheres in 2153, when Enterprise NX-01 entered the Expanse in search of the Xindi. The first sphere they came across was being used as a base for Osaarian pirates. Enterprise engaged in battle with an Osaarian vessel within the cloaking barrier of the sphere, and was able to take a series of detailed scans. Quantum scans of the sphere indicated it was nearly one thousand years old. (ENT: "Anomaly")
Upon further investigation, the Enterprise crew was able to determine that the spatial anomalies which riddled the Expanse occurred at points where the waves of gravimetric energy being emitted from the spheres intersected. This led T'Pol to hypothesize that the spheres were created for the express purpose of creating the Expanse. Enterprise later encountered the Triannons, who held that supernatural beings whom they referred to as "the Makers" had created the spheres to reconfigure space in preparation for their eventual return. The Enterprise crew later discovered that the Triannon myth was based in fact, and that the spheres had been created by a race of trans-dimensional beings who were attempting to make the Expanse habitable for their species as a prelude to invasion. (ENT: "Exile", "Chosen Realm", "Harbinger")
Captain Archer learned from Daniels, a temporal agent from the 31st century, that, in the 26th century, the Expanse would grow to encompass fifty thousand light years of the Milky Way Galaxy, and that the Sphere-Builders were trying to manipulate the Xindi into destroying Humanity in an attempt to prevent the founding of the United Federation of Planets, which would ultimately defeat the Sphere-Builders. With this information, Archer was able to form an alliance with some of the Xindi against the Sphere-Builders. (ENT: "Azati Prime")
The crew learned from Degra that the spheres were controlled by a network of artificial intelligence, and that each sphere held a redundant memory core. A team from Enterprise was able to gain access to the interior of a sphere through an exhaust port which was holographically disguised. The team was successful in retrieving the memory core, but not before Corporal Hawkins was killed by an automated defense system. (ENT: "The Council")
With the information retrieved from the memory core, T'Pol was able to determine that each sphere was connected by an interspatial manifold on its surface, and that four of the spheres were integral to the connection. Enterprise was able to disable the manifold of the sphere designated "Sphere 41" with a deflector pulse, causing a chain reaction resulting in the destruction of the entire sphere network, and eliminating the spatial anomalies in the Expanse. (ENT: "Zero Hour")
Spheres encountered by Enterprise Edit
- Sphere 1. This sphere, encountered in September of 2153, was being used by Osaarian raiders as a base. It was located in the Orassin distortion field. (ENT: "The Xindi", "Anomaly")
- Sphere 2. Sub-Commander T'Pol theorized the existence of this sphere, located not far from Tarquin's planet, and turned out to be correct. Its level of gravimetric energy was much higher than that of Sphere 1. Captain Archer and Commander Tucker took detailed measurements of this sphere in a trellium-lined shuttlepod, as Enterprise could not get close to it. These measurements allowed T'Pol to calculate that there must have been at least fifty spheres in the Expanse. (ENT: "Exile")
- 12th Sphere (Triannon designation). This sphere was 6.3 light years from the Triannon homeworld. D'Jamat's ship had been on a pilgrimage there for several months when discovered by Enterprise. As far as Enterprise could establish, it was completely identical even in the smallest details to sphere 1 and 2. (ENT: "Chosen Realm")
- Sphere 41. T'Pol determined that this sphere was a key to the sphere network's energy grid, and with Commander Tucker, developed a means of destroying it using Enterprise's navigational deflector array. This plan was successful, and triggered a chain reaction, destroying all the spheres within the Expanse. The destruction of the spheres returned the Expanse to normal space, devoid of anomalies. (ENT: "Countdown", "Zero Hour")
- Enterprise rendezvoused with Degra's ship behind the cloaking barrier of a sphere so that Captain Archer could show Degra and Jannar evidence of the Guardians' duplicity. It was not far from the Azati Prime system and about a dozen light years from the Xindi Council planet. (ENT: "The Forgotten")
- A sphere just outside the solar system containing the Xindi Council planet. An Enterprise team went inside it to steal its redundant memory core. Corporal Hawkins was vaporized on the mission. (ENT: "The Council")
- The Sphere-Builders used a sphere to generate anomalies to protect the Xindi weapon from an attack by the Arboreals, Primates, and Aquatics. (ENT: "Countdown")
Background information Edit
In the final draft script of "Anomaly", the first description of a Delphic Expanse sphere's exterior referred to it as "a large, gleaming, METALLIC SPHERE the size of a small moon." In the final draft script of "Exile", the exterior of another sphere was initially described in much the same way as that of the first sphere, except it was referred to as "giant" rather than "large". The same script additionally described the exterior as "sleek" and "a vast, gleaming, metallic landscape with a mild but noticeable curvature." In the final draft script of "Chosen Realm" (which was initially called "Untitled Sphere Story"), another of the spheres was described as "vast, metallic, mysterious, hanging in space."
The interior of the sphere, in the final draft script of "Anomaly", was described as a "dark, cavernous interior" which was absolutely enormous and "easily spans a major metropolis." The script continued, "At the CENTER of the Sphere, we see an assembly of SEVEN exotic, high-tech STRUCTURES that tower outward in various directions. Only three of the towers are ACTIVE, PULSING with POWER like some kind of skyscraper-sized nuclear reactors; the other four are dark, inactive. A deep, percussive RUMBLING sound echoes through the interior."
The usual appearance of a Delphic Expanse sphere's exterior was designed by production illustrator John Eaves. He drew a total of six concept sketches before the fourth one was approved. The first of these proposed designs was heavily influenced by the look of an unapproved initial design for the Suliban helix, illustrated earlier in the series run of Enterprise. "The first drawing of the sulibon [sic] helix ship had this sphere drawn in as the core of the ship," recalled Eaves. "When it came time for the xindi sphere's to go in for approval I borrowed the sulie core and offered it as a choice." The sketch for the sphere even had a massive opening that, in the original Helix design, had been intended to allow access for Suliban cell ships. 
The sphere's interior was designed by Doug Drexler. He later explained that an early digital concept painting for the sphere's innards had "a more linear and 'constructed' looking central core" than the final design, which instead looked as if it had been grown. Not only was the accepted design generally approved but Drexler himself preferred it. "Frankly, I really wanted to do the organic looking one because it reminded me of Vgr," he reminisced. After being given the go-ahead, the digital artwork was delivered from the art department to Eden FX, by whom it was then adapted for television usage. Drexler also created a cutaway view of a sphere, showing the seemingly organic interior beneath a portion of the sphere's outer skin. (X)
The Delphic Expanse spheres were visualized almost entirely with CGI. Green-screen was used for some shots of environmental suited Enterprise crew members walking on one of the spheres. "Their entire environment is created by us. There's nothing practical," explained Director Roxann Dawson, during production. "It's all created by visual effects. So, in order to do that, it has to be planned with everyone in mind, so that we all know what we're doing on shots like that." ("A Day In The Life Of A Director - Roxann Dawson ", ENT Season 3 DVD special features) For foreground portions of a sphere's interior in the episode "Countdown", large metallic-looking set pieces were reused, having been created for the earlier season three installment "The Forgotten" to represent parts of the Enterprise's hull. The pieces were re-detailed for their inner-sphere usage and later went on to be included in the interior set for the Xindi weapon. (Star Trek: Communicator issue 151, p. 59)