Commorragh
Overview
Commorragh, the Dark City is the capital of the Dark Eldar society. It's located deep within the labyrinth of the Webway, the space between the Materium and Immaterium.
Background
There are many rumors about Commorragh, the terrifying home of the Dark Eldar, making it difficult to know just what is truth, and what has been fabricated by the shattered psyches of those unfortunate enough to find themselves in Commorragh.
Founding
Commorragh has stood for over ten millenia, and due to the difficulties of surviving the Dark Eldar way of life, combined with needing to live much longer than what is considered possible for normal Eldar, there is only one being who could possibly remember the founding first-hand: Asdrubael Vect, Supreme Lord of the Kabal of the Black Heart. In fact, Vect claims that he is the founder of Commorragh, as well as the one who discovered the way of extracting souls from living creatures in order to prolong one's life. Unfortunately, he is the only one nearly ancient enough to know whether these statements are true or false, so the validity of this claim is unknown.
Location
Commorragh was built in the Webway for a number of reasons.
First and foremost, it is a dimension where the forces of Chaos, and specifically Slaanesh, have very little influence. Therefore, the Webway is the location where The Thirst takes its toll the least on the Dark Eldar.
Secondly, the fact that the Webway connects virtually to everywhere in the galaxy makes it ideal as a staging point for raids on other races. It's not uncommon for a raiding party to be able to run raids on an entire solar system before the Imperium is able to respond, and they have no method with which they can traverse the Webway, so the raiding party can travel back to Commorragh undisturbed.
Finally, the infinitely large expanse of space makes it the perfect place for a city the size of Commorragh. No single planet would be capable of supporting the sheer size of the Dark Eldar people, and no system of planets could ever hope to be as defensible as the Webway allows Commorragh to be.
Scale
The immensity of Commorragh has never been explicitly detailed, but if you look at the historical records of the Eldar civilization prior to the Fall of the Eldar, you can get an idea of the necessary size.
Before the birth of Slaanesh, the Eldar were said to number in the trillions. Only a small fraction of these untold trillions of Eldar held a distaste for the hedonistic pursuits of the masses, and only that fraction left to become the Exodites and Craftworld Eldar. The birth of Slaanesh was indeed felt by all Eldar as a drain of their soul energies. But, of the Eldar who remained, those on the fringes of the Eldar Empire that were the youngest and most virtuous were not destroyed outright, simply weakened by this psychic assault.
It is these survivors that make up the Dark Eldar ranks. And if one were to consider statistical probability, the number of Dark Eldar could be considered no less than 500,000 strong. Assuming the Eldar Empire numbered two trillion, then positing that due to the extremely long life of the average Eldar, there would be on average one hundred generations worth existing at a time, then having only the youngest five generations survive, the number would come to one hundred billion. Then assuming there were 1000 planets in the Eldar Empire Asdrubael Vect was on only one, and in only one city. Dividing one hundred billion by 1000 brings us to 100 million. Then finally assuming that there were one hundred cities on each planet, this brings the number to 1 million subtracting those that were killed or driven insane afterwards brings about half a million.
Regions
Commorragh is split up into regions, and these regions are controlled by Kabals. Members of those Kabals live in and police these regions, as the existence of their Kabal depends, to a large degree, on maintaining districts for its members to live in. Traditionally, Wych Cults maintain Battle Coliseums in the districts of Kabals they're allied with, Haemonculi are given laboratories (usually underground) within the districts of Kabals they provide their services to, and Mandrakes will be given the right to prowl the streets and alleys in search of meals so long as they agree to assist the Kabal of the region when requested.
