The Citadel, technically known as the United Nations Continuity-of-Species Bunker (UNCSB) is a massive structure built under the Canadian Shield - one of the densest geological structures on Earth. Begun in 1960, the Citadel was designed as a response to the near-extinction of humanity during the Human-Sen'kaal War; that is, as a practically impenetrable last refuge for humanity in the event of a total defeat of human military forces. The Citadel is also noteworthy for being the largest, longest-running, and most expensive construction project in human history (As of 2013, it is still only 89% finished.)