The Hierarchy of Cissilith
The drow of Cissilith follow the matriarchal traditions of their ancestors to an extreme degree, and worship their serpentine goddess Ssa with a fanatical devotion. Ssa teaches the values of subtlety and raw ambition, and therefore the society of Cissilith is fueled by espionage and clandestine murder.
The city is divided into a large number of noble houses, which can range in size from hundreds of members in the most powerful houses to mere dozens in the weakest. The power and prestige of noble families are seen as a gift from Ssa herself as a reward for their cruelty and raw ambition, and thus the most cruel, murderous, and ambitious drow are the ones with all the power. However, it is seen as crass, almost cheating, to commit murder openly in a brash and bloody display is more likely to see the murderer killed in turn than it is to gain standing for her.
Nearly every drow who lives in the city works for a House, and every house is as self-sufficient as possible. Each house is ruled by a single matriarch, whose lieutenants are her daughters, with her granddaughters and their descendants serving in lesser roles. At the lowest levels, including guards, artisans, and soldiers, adoptees who are unrelated by blood often find work within a noble house, but those unrelated to the matriarch will almost never rise to any level of real authority. Power is strictly hereditary, so a daughter wishing to seize the reins of a house is likely to commit a quiet matricide to achieve her aims. If she is a younger daughter, she will have to slay several of her sisters as well.
There is a tendency in Cissilith to misconstrue the presence of an oura’thir as a gift from Ssa, rather than Kestali (who the drow of Cissilith believe, by and large, has abandoned them). Every effort (sacrifices, offerings, and prayer) is made by the Matron of a house to obtain for herself the honor of an oura’thir companion, and if possible she procures them for her daughters as well, both because they are powerful weapons and because having even one is a sign of Ssa's great favor (or so they believe.).
Below even the guards are the slaves, tasked with the most menial, disgusting, and boring of tasks with which a drow should never dirty their hands, no matter how lowborn they might be. Some slaves are drow, but are afforded no greater respect than the other races held in bondage. They, after all, are failures of the highest order and are hated by the beloved goddess Ssa for their weakness and ineptitude, etc.
The most powerful house in the city, currently House Hunarn under Matron Balxae Hunarn, guards access to the Serpent's Font, the city's one well of potable water. Those who fall into disfavor are denied access to the house's grounds, and therefore the well. This cruel punishment condemns the family so cursed to choose between exile or a slow death by dehydration, because drinkable water is often too difficult to find in the duskmere for them to stay. (There are swamp-folk and nomads who live there, but they have enough contempt for the nobility of Cissilith that they're not likely to be of any great help)
Every house would dearly love to gain favor in the eyes of the goddess Ssa, who guards her city and people jealously and rewards her most beloved richly. They would also love the security of having unrestricted access to the Serpent's Font. In order to wrest favor and power, both very finite resources in Cissilith, from their rivals, their only course is to discredit them (usually by framing them for a particularly inept murder, or for blasphemy to Ssa), or to kill each and every one of them to the last babe in arms without getting caught. When this happens, the victorious house will often assimilate non-blood members (servants, infantry, slaves, etc.) into their own ranks, allowing these low-born to keep their homes and possessions. This greatly eases the transition into the new holdings for the nobles and helps to ensure the loyalty of their new hires.
Such is the way of things in Cissilith.