As the Priests analyzed the data, one trajectory after another was marked out.
One particular report even contained intelligence that shocked Guilliman.
Someone had sighted a vast space fortress, as immense as a mountain, bearing the insignia of the Dark Angels and ancient buildings.
After carefully recalling every potentially relevant piece of information, the fortress's identity became clear.
Rock Monastery.
This made Guilliman acutely aware that something extraordinary was happening.
The Dark Angels had moved even the Rock Monastery here. Clearly, something of great importance had arisen.
Unlike the other Chapters, the Dark Angels had long since lost their Homeworld, Caliban, and the Rock Monastery had once been their base on that world.
After Caliban had been shattered completely, the Dark Angels had salvaged their base along with the land beneath it, turning it into the present-day fortress known as the Rock.
This enormous space fortress had an entire section of Planet's surface as its foundation, making it vast and sturdy.
And this urgent muster, undertaken regardless of cost, had left numerous traces.
More and more information was compiled, all of it pointing squarely toward the western reaches of the Ultima Segmentum on the dark side, a mysterious region not far from the Great Rift.
Many new Star Systems had appeared in this region that had never been discovered before the Great Rift opened.
Since the launch of the Indomitus Crusade, many Imperial scholars had studied this phenomenon, and their eventual conclusion pointed to the sudden opening of the Great Rift.
Many of these Planets had likely been swallowed by the Warp long ago, then drifted through that unreal expanse of space.
When the Great Rift opened, these Planets had been expelled from the Warp and eventually stabilized once more in realspace.
The point where the courses of numerous Dark