Heian
From Halopedia, the Halo wiki
This Unnamed Planet was a world in the Milky Way Galaxy. The planet was terrestrial, with a breathable atmosphere and an Earth-like surface. Meteor showers were common on this world.[1]
History
At some point predating both Humanity and the Covenant, the planet was inhabited by a yet-unknown civilization. They likely vanished at some point, as their cities were abandoned, yet mostly intact, by the 26th century. Strangely, the architecture of the structures greatly resembled ancient Japanese architecture on Earth. Despite this, it is possible that they were somehow related to the Forerunners.
During the Human-Covenant War, the world was the site of an important Covenant logistics base, from which supplies were delivered to the rest of the planets in the system, as well as the entire sector. The UNSC deployed a team of ODSTs and a Spartan on the planet, with the mission to assassinate the Prophet in charge of the Covenant base, in order to stop the Covenant supply chain. They were also tasked with photographing the unknown ruins. The team succeeded in their mission, despite the loss of the Spartan and one squad member.[1]
