Elysium City
From Halopedia, the Halo wiki
Summary
Elysium city was the city in which John-117 grew up, before he was chosen for the Spartan-II project and replaced with a flash-clone.
Very little is known about the city itself, or John's past in the city, but Elysium has strong links with the trends of the Halo series, especially through it's name. Elysium was a Latin word to describe a paradise, where heros and warriors went after death. It can be likened to the modern conception of heaven.
