Sagittarius Arm

The Sagittarius Arm is a minor spiral arm of the Milky Way galaxy. It lies between the Scutum–Centaurus Arm further toward the galactic core and the Persus Arm further toward the outer rim. The Orion Arm, or Orion Spur, branches off from the Sagittarius Arm.

History
The Milky Way's Sagittarius Arm was explored by the Forerunners thousands of years ago and at least two shield worlds were constructed in distal star systems of this arm. Both shield worlds 006 and 10021 were built under the direction of Warrior-Servants during this time, with the former being constructed in the Zeta Doradus system. Prior to the firing of the Halo Array in 97,445 BCE, the rings known as Installation 01 and Installation 07 were transported from Installation 00 points in the Sagittarius Arm. Installation 01 was placed at the Array's Beta position distal to the the offshoot of the Orion Spur and Installation 07 was placed at the Zeta position, proximal to Orion. It was from these locations that Beta Halo and Zeta Halo killed every unprotected life form with even the most rudimentary of nervous systems within twenty-five thousand light-years of each.

At the end of the twenty-fifth century, the planet Onyx, which hid Shield World 006, became the subject of focused investigation by the United Nations Space Command. The Office of Naval Intelligence went on to use Onyx to host its top-secret Spartan-III program. Following a large 2543 battle in the Psi Serpentis system between UNSC Battle Group India and two Covenant fleets, scattered reports of independent human forces fighting the Covenant began to pop up on the outer edge of what the Office of Naval Intelligence believed to be nonsanctioned human conolnized space. These reports tracked toward the Sagittarius side of the Orion Spur. Near the end of the war between the Covenant and humanity, a battle was fought at Onyx. Following the conflict's conclusion, Shield World 006 became the subject of human exploration and an agreement between the Unified Earth Government and the Swords of Sanghelios resulted in a select group of humans, Sangheili, and Unggoy living within the shield world together. Installation 07 was discovered by humans a few years after the war and before long the UNSC dispatched of researchers to study it. When the rogue artificial intelligences calling themselves "the Created" attempted to seize power throughout the galaxy, Shield World 006 was pulled beyond their reach by being hidden within a small slipspace bubble.

Locations
The Sagittarius Arm holds a number of Forerunner constructions. Proximal to the Orion Spur lies Installation 07. Shield World 10021 can be found just beyond the Orion-Sagittarius junction and further beyond it are Installation 01 and then the Zeta Doradus system, home to Shield World 006.

Gallery
 File:XF-063 04-02-2491 150x150 p1.png|The arrow points to the location of Onyx within the Zeta Doradus system. File:H5G - Milky Way.png|The Covenant was evidently familiar with a number of locations in the Sagittarius Arm. 

List of Appearances

 * Halo: Ghosts of Onyx
 * Halo 3
 * Remember Reach
 * Birth of a Spartan
 * Halo: Evolutions
 * The Impossible Life and the Possible Death of Preston J. Cole
 * Halo: Glasslands


 * Halo: Hunters in the Dark
 * Halo 5: Guardians
 * Halo Mythos
 * Halo: Fractures
 * Lessons Learned
 * Halo: Legacy of Onyx