Battle of the greater Ark

The Battle of the greater Ark was one of the last battles in the Forerunner-Flood war, fought around the greater Ark.

Background
The greater Ark, the original Ark installation and the primary facility of the Conservation Measure, had become the last line of defense for the Forerunner ecumene after the Forerunners were forced to abandon the galaxy itself in the face of the unstoppable Flood onslaught. However, the placement of all Forerunner governing functions, strategic command and the majority of their population as well as military forces also made it an attractive target for the Flood, which could, through a concentrated assault, deliver a crippling blow to their enemy.

The battle
An enormous Flood-controlled fleet coordinated by the Graveminds and the traitorous Forerunner AI Mendicant Bias, supported by numerous Precursor star roads, attacked the greater Ark and the nearby Omega Halo, the last of the original twelve Halos. Despite the Forerunners' efforts at defending the greater Ark with their remaining military assets, their forces were quickly overwhelmed by not only the Flood's vast numerical superiority but also the power of the star roads. Although Omega Halo was fired, decimating a small portion of the star roads as well as purging the satellite galaxy of Path Kethona of sentient life, the star roads soon destroyed both the Halo and the greater Ark.

Aftermath
The battle marked a catastrophic defeat for the Forerunners, who lost the vast majority of their remaining population, leadership, and military strength. Additionally, a large portion of the Lifeworkers' biological samples of the galaxy's species stored on the greater Ark and Omega Halo were lost; in addition to the destruction wrought by the star roads, the Ur-Didact used a Composer to harvest Omega Halo's sizable transplanted human population, severely complicating the Librarian's plans for mankind and the galaxy on the whole. The Librarian and her aide, Monitor Chakas, managed to salvage a few of the specimens; Chakas also saved a handful of Forerunners, including the IsoDidact from Omega Halo, aboard a Gargantua-class transport. Using coordinates provided by the Master Builder, Faber - killed during Omega Halo's destruction - the few survivors traveled to Installation 00, the lesser Ark, its location still secret from the Flood. Soon after, the final Halo Array would be distributed across the galaxy and fired by the IsoDidact, starving and eventually halting the Flood.