Tau and chaos make gains on Ergura's Fall

On Haven, the Tau and chaos forces had already landed significant forces by 11.022M42 and it was only a matter of time before the two forces met. In addition, the Tau had been excavating and exploring ancient necron ruins and this, along with the desire by the Imperium to establish their own base of operations on the world led to a series of confusing engagements as 11.022M42 approached its end.

The encroachment on necron tombs led to a running battle between the Tau and small forces of necrons as the tombs tried to defend themselves. Although completely opposed to the necrons, the Imperium sought to take advantage of the difficulty the Tau now found themselves in, and sent a force of Adeptus Custodes to fight alongside the ancient aliens. There was no real "alliance", but the combined forces of the necrons pushed the Tau back for now, enabling the Imperium to thwart Tau exploration south towards their own base.

Later, the Tau clashed with the forces of chaos as they expanded their patrols west, and the chaos forces reacted by summoning a large force of khornate daemons, wiping out the Tau assault force. The Tau had been frustrated in their attempt to move south and west, but found more success in their move to the west. Here, there were no chaos or imperial forces and the only army standing in their way was a necron phalanx who were attempting to prevent yet more Tau incursions onto their tomb complexes. This time the Tau were successful, obliterating the necron army and looting the tomb complex.

By the end of 11.022M42 the Tau had managed to establish the largest force on Haven, but were now vying with the forces of the dark gods for domination of the world.