The song combines deep strings with a piano rhythm to create an imposing, suspense filled piece. Towards the end, a higher string set creates a building crescendo, accompanied by a vocal set reminiscent of the one at the end of The Last Spartan.
Though its title suggests its association with New Mombasa, the 'Earth City', it is frequently played as the theme of the Covenant's Scarab walker. It is first played in the Halo 2 E3 2003 demo when John-117 mans the gun of a Gauss Warthog and continues on until the end of the demo. This is the only time when the music is not associated with the Scarab. It first appears in the final game when the Pelicans launched from UNSC In Amber Clad encounter the Scarab in the cinematic before Outskirts. It is later played during Metropolis when John-117 encounters Wraiths outside a Marine Command Post, just after a Scarab passes through. Shortly afterward, it is again played as the Prophet of Regret's carrier prepares to make a Slipstream Space jump, while the In Amber Clad attempts to intercept it.
The song's length is 3 minutes and 6.54 seconds (3:06.54).
The version played during the Metropolis level is somewhat different than the OST version.
In the Halo 3: ODST Original Soundtrack, a similar song, called "Orbital Drop Shock Troopers" is in the track Finale. This song is played during the level Coastal Highway, and, like Earth city, is played during a Warthog chase within New Mombasa.