Metarchy

The Metarchy was the governing ancilla network of the Forerunner Capital world Maethrillian, managing its various domestic and defense systems, including the Capital's sizeable defense fleet. A vast interconnected network consisting of trillions of ancillas, the Metarchy was overseen by a Metarch-class ancilla, one of only five active at the time.

Forerunner-Flood War
The Metarchy was active during the trial of the Master Builder, but was subverted early in the proceedings when 05-032 Mendicant Bias arrived at Maethrillian with a stolen Halo ring intent on wiping out the Forerunner leadership. Disabling the governing Metarch-class ancilla, Mendicant began systematically suppressing all other ancillas present on the Capital, and locking up the armour of many Forerunners on the planet.