"If there was one crown jewel that lit brightly in the see of broken glass that was the Outer Colonies, it would be the fortress world of Chi Rho. That tells you enough why the CMA should've been put on a leash long ago."
―Anonymous naval captain.
Chi Rho is a major UEG colony located in the Ectanus 45 system. It was part of a thin belt of worlds that separated then Inner and Outer Colonies informally referred to colonists as the "Middle Colonies". Considered the gateway to between the two regions, the colony's strategic location would see it becoming the capital world of the Colonial Administration Authority and it's subbranch the Colonial Military Administration. This heavy military specialisation saw it become a major base for the UNSC, who used it to springboard their forces from the Inner Colonies into the Outer Colonies. The large military presence, especially during the Human-Covenant War, earned Chi Rho the nickname the "Reach of the Outer Colonies". In 2535, it was the site of the Siege of Chi Rho, where UNSC forces dug into the planet's crust and held out for months against the Covenant onslaught before finally falling.