Population Migration / Travel
The Empire consolidates its power in the First Horizon. The mystics later known as the Symmetry start to colonize the Second Horizon.
The two first Horizons were colonized long before the Third Horizon. The eternal Emperor of Ardha rules the First Horizon, or Terra as it is known there. The Second Horizon was dominated early on by the Symmetry, a caste of mystics. They had fled the tyranny of the First Horizon and colonized the Second Horizon in a series of quick waves. The Symmetry practitioners developed their own political dominance in the Second Horizon to protect themselves from the Emperor.