Ertshea

Ertshea was a planet placed under the protection of the Galactic Heritage. (PROSE: The Tomorrow Windows) It was home to the Wizards of Ertshea. It was one of the planets that the Greth attempted to invade, later claiming the title of "Scourge of the Wizards of Ertshea". (PROSE: Out of the Box)

Behind the scenes
The name is reminiscent of, the setting of Ursula Le Guin's highly influential. The reference is most pointed in Out of the Box which makes reference to "Wizards" of Ertshea: one of the most notorious Earthsea book was entitled.