Chi Rho

Chi Rho was an UNSC colony world in the Ectanus 45 system that was said to separate the Inner Colonies from the Outer Colonies

History
In 2535, during the Human-Covenant War, following the loss of most of the Outer Colonies, refugees had started flooding the planet and all available space was being used for victory gardens and refugee camps. Vice Admiral Jean Mawikizi resolved to make a stand against the Covenant on Chi Rho, digging in deep within the planet's crust to survive a glassing attack, forcing the Covenant to come down and flush them out man-to-man.