Milgrief is the dumping area for the rest of The City and simultaneously acts as the central base for the Revolutionaries. It was originally built underground to be the wasteland after space on the surface started to run out; as a result of being underground, all natural light is restricted from entering.
After tension broke and people were forced to evacuate due to The Campaign, Milgrief was the only place that they could turn to. As more and more people started to pour into Milgrief and out of the rest of The City, they started to build a town of their own. The rebels used the rubble and scrap they found in the wasteland to build any shelter they could. Unfortunately, many of the outlets that were produced became corrupt and without any form of law to keep people in order, many fell to thriving illegally by selling things such as narcotics and even women. Most people split themselves into different sectors and are recognised as different districts. Unfortunately, some people couldn't agree on appropriate methods to move against the government and certain districts fell out with one another. Gangs started to form and civil outbreaks became a common thing.
It's not unusual for government spies to slip into Milgrief to keep their eye on any possible threats that may rise and also cause chaos while they're there. The most recent part of the governemnt's agenda includes kidnapping young children from Milgrief in order to bring them up to the higher levels and corrupt them into turning against their family.