851 BCE

The year 851 BCE is a year in the 850s BCE in the 9th century BCE.

Unknown

 * During the first Age of Reconciliation, the Covenant face rebellion by Sangheili heretics opposed to the Writ of Union. Under the leadership of Ussa 'Xellus, the heretics known as the Ussans depart from Sanghelios to Shield World 0673 in order to seek sanctuary from the Covenant.