Agon Nine was absorbed into Xim's empire as he expanded his borders from the Kingdom of Cron in 25,127 BBY. With the collapse of the empire, Turallon would be forgotten for several centuries, until after the Great Hyperspace War, it was discovered by Galactic Republic scouts.
Unfortunately for the forgotten world, the Confederacy of Independent Systems discovered routes into the system during the Clone Wars and invaded the planet Iego nearby. Trapped in Separatist space, the world managed to avoid the war until the formation of the Galactic Empire in 19 BBY. Because of its distance from the Core and its relation to the CIS, the newly formed Empire established penal colonies on the planet's surface, imprisoning prisoners of war and other traitors from the War. Shortly after the Battle of Murkhana was won, Darth Vader planned to incarcerate captives on Agon Nine personally.
Some Clone troopers who disobeyed order 66 were sent to the prisons on Agon Nine as well.