First Illumination

The First Illumination, formerly known simply as the Illumination, was a series of reforms and military campaigns in the Covenant's High Antiquity, generally agreed to have spanned from the 3rd Age of Reclamation to the 7th Age of Doubt (circa the 1st century BCE to the end of the first century CE). It followed the so-called First Interregnum, a period of political fracturing that had left High Charity's cultural and political power considerably diminished while the holy city spent decades at a time on long journeys in the greater galaxy. The First Illumination saw the holy city returning to the Covenant Sphere and re-establishing control over the disparate worlds that had drifted apart under the rule of Sangheili vassal-kings.

If the Writ of Union marked the creation of the Covenant, the First Illumination is often credited as having given rise to many of the the hegemony's central institutions and organizational practices, some of which would endure up until the Great Schism. One of the era's major reforms was the establishment of the so-called theme system as a means of partitioning the Covenant Sphere, although this would eventually diminish in the lead-up and during the Feudal Period and eventually be replaced by the domains as the Covenant's primary provincial units. The full extent of the Holy Ecumene at the time was also first mapped by High Charity's cartographers during this period.

The name First Illumination was given retroactively during the Second Illumination as the Hierarchs of the latter era sought to recapture the significance of the earlier consolidation. Although Covenant popular historiography typically portrays the First Illumination as a singular, contiguous string of events, several historians have noted that it is more likely that the various reforms and conflicts were more spread out across time, and those living during the so-called Illumination would not have regarded it as one continuous event.