Scale of Third Sphere

Hundreds of expeditionary forces set out in every direction from the Tau sept worlds, each explicitly tasked with the assimilation or subjugation of a chain of star systems deemed desirable by advanced scouts and long-distance surveillance drones
...
 The Tau Empire expanded at an incredible rate. Within the first year, several potential sept worlds had already been established, wrested from Ork warlords or other xenos species and colonised within weeks of conquest.

Warzone: Damocles pg. 7