From Halopedia, the Halo wiki
Mahsko is the Banished name for a seaside region of Installation 00. It is the site of a massive Forerunner city built atop a cluster of seven basalt sea stacks arching toward a large peninsula. Each rock column is connected by delicate-looking transport conduits. The Forerunner Dreadnought rests among the structures built upon one of these sea stacks. As of June or July 2559, the region was uncontested as neither the Banished nor the crew of the UNSC Spirit of Fire had yet to lay claim to it.
Battle for the Ark
After the Prophet of Truth used the Anodyne Spirit to travel to the Ark, the vessel landed amidst the city that crowned one of Mahsko's enormous sea stacks. Unbeknownst to the Prophet, the Keyship's automated landing was actually facilitated by the fragment of Mendicant Bias stored within the vessel. By landing here, Mendicant Bias was reunited with the rest of its intelligence that had rested on the Ark since the end of the Forerunners' war with the Flood.
A new conflict
In the midst of the Second Ark Conflict in 2559, the Banished visited Mahsko with the intent of infiltrating the Keyship and retrieving shards of a slipspace flake held within. Fighting through loyal Covenant warriors that had remained within the vessel for the past seven years, the Banished force was ultimately successful in their mission. With the shards in hand, they retreated to safety, now knowing that Covenant forces still occupied the Anodyne Spirit.
List of appearances