From Halopedia, the Halo wiki
Path Nachryma was the Forerunner name for a region of space in the Milky Way galaxy, located in close proximity to the Orion complex. It was a tight cluster of over a hundred old stars located in Thema 102 and contained a once heavily populated system of dozens of worlds, one of which was ringed with icy moons. According to Mendicant Bias, the ring of moons contained a slipspace portal to the greater Ark that was always open. After being captured by the Flood in the final years of the Forerunner-Flood war, Catalog was taken aboard a subverted Fortress-class vessel that traversed a system it identified as part of Path Nachryma. Due to a lack of Forerunner resistance, the Juridical entity believed that a battle between the Flood and the Forerunners had previously occurred in the system. Mendicant Bias and the Gravemind present on the Fortress-class vessel planned to use the portal present in the system to mount an attack on the greater Ark.
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