Installation 04

The Forerunners thought they were so clever when they built this place. Ooh, they said, lets build a weapon that can wipe out all life in the galaxy, just to destroy a Tier 7 life form. And so they did, but instead of killing off all the Flood they said, hmm, these little guys are actually pretty cool, lets keep them on the weapons we used to destroy them so that they will not go extinct and are in a great defensive position against anyone who doesn't want to harm the rings...

Guilty Guilty guards this ring, and he doesn't like it when people unleash the Flood.

and his pals onboard the Pillar of Autumn crashed onto this ring, an after a long four-way battle between Humans, Covenant, Sentinels and Flood the rings was destroyed. However, The Ark began constructing a replacement ring which was dubbed Installation 04B. This ring was identical to its namesake, but it was not finished by the time Johnny and Co. found it. They fired the ring to destroy the Gravemind, but destroyed both The Ark and the ring in the process. Luckily, the Gravemind's poetry survived this catastrophe, so he was able to rebuild himself on what remained of Low Charity.