Far out from the standard transportation and trade routes a until now hidden system is found.
A star system with five planets, an asteroid belt and several small planetoids at its outermost edge.
The Imperium had here found a perfect planet, green and full of jungles and vegetation. A Garden of Eve if you will. The initial intel sweeps from the Magos Biologis of the Mechanicus shown no intelligent native species.
With no enemy activity in the system of any kind, an order of colonization and industrialization is issued.
This virgin planet was named Sertoria Comitus.
Deeper in the denser part of the jungle ancient temples and strange totems were found, to the colonist unknown designs or origin. These most be of a long lost civilization of some kind.
Hundred and twenty standard years after the first step of human colonization, the planet was attacked.
An all-out attack on the planet is initiated and the Planetary Defense Forces are pushed back and much of the development and urbanizations are bombarded and destroyed.
The xenos are described as extremely fast and sleek, and utterly brutal and shows no regards for the human inhabitants of the planet, rather the opposite with almost hatred
The alarms reaches the Imperium and prepare movements of troops to help out with the defense and a counterattack.
Death Korps of Krieg forces from the 317th Grand Armeé are amongst the forces responding and are deployed and prepared for war.
The conflict would be known as the "The Reconquest campaign of the Sertoria Comitius" in the eyes of the Imperial scribes.