I’m replaying the mission Shutdown in Halo 4 and looking at the various Forerunner structures below the level.
Do we know the purpose of these structures?
In the beginning of the mission Requiem we see a similar structure. I believe that one is different than the one Shutdown takes place above, but perhaps the Requiem one is one of the smaller structures in the distance?
I think it’d be great to have a world map of Requiem and see everywhere Chief and Cortana traveled on the planet.
We don’t know what all the Requiem structures are, but In-game video terminals in Halo 4 provide the basic back-story of the Didact and Librarian during the Human-Forerunner War and then the Forerunner-Flood War.
In the final terminal cutscene, after stunning the Didact with a lightrifle before she locks him in the Cryptum, the Librarian says the floating towers we enter in the Shutdown mission (below) are the Indexes in which all lifeform samples from the galaxy (including humans) were stored to protect them when the Halo Rings fired 100,000 years ago to wipe out all life in the galaxy to stop the Flood. So the ground structures are like a “storage silo complex” for the Indexes.
Meanwhile, as the Reclaimer, presumably Chief has found a kind of “home” for the humans which had been genetically modified with the Forerunner Genesong to reseed humans on Earth, the human line Chief and his Genesong evolved from, even as the Librarian will finally activate Chief’s Genesong on Requiem in the Reclaimer mission. So, as Cortana says above Earth “Welcome home, John” for Chief’s humanity, so Requiem is “Welcome home, John” for Chief’s Forerunner Genes…
https://www.youtube.com/watch?v=ZLOz8UrIJBo&t=872s
This links into this video terminal cutscene from Halo CE Anniversary, showing scenes from the line of ancient humans to Chief…
https://www.youtube.com/watch?v=TyKoYmgD_tQ&t=35s
YouTube videos exist to help find all the hidden video terminals, else anyone can just watch the whole video above for the back-story of Requiem, the Didact and the Composers in Halo 4, of which only a small summary is given to Chief by the Librarian in the Reclaimer mission cutscene.
Hope this helps.