Unidentified Forerunner planet

This Unidentified Planet was a world previously occupied by the Forerunners prior to the Flood invasion, culminating in the Forerunner-Flood War. The surface of the planet was covered in massive Forerunner structures and glyphs.

Trivia

 * The Forerunner symbol for the number "0" appears throughout the planet's surface. This is also the symbol for the Iris campaign.