Imperial assault on Corticant ends in disaster

In early 020M42 with the war on Mordecai stagnating and the necron device on Hexis lost, Lord General Militant of the Aleph Sector, Justinian Flavius Maximus, having now been in position for some time, was growing increasingly concerned over the strategic situation in the Perseus Deeps. 

The main passageway through the Cicatrix Maledictum - the Foramen - was held open by the active necron device at Corticant. The invasion of Tarlius had secured the passageway for the Imperium, but the device itself was still under the control of the eldar. At any time the xenos could, should they do wish, shut down this device and plunge the entire sector on the wrong side of the divide into ruin. For now the eldar seemed content to keep the Foramen open, as the war against chaos was aligned with their own strategic aims. However, being beholden to the aliens was unacceptable to the imperium, and Maximus ordered the retaking of the device chamber on Corticant. 

The Hammers of the Emperor accepted the mission, and sent strong armoured formations along the road from Lochford to the excavation site on Corticant. Significant xenos forces appeared to bar their way, including a host of wraithguard and a towering wraithknight. Along side these eldar forces the astartes noticed the presence of Drucharii, suggesting the Aeldari race were united in making sure the device remained under their control. 

Savage fighting developed in the valleys on the approach to the excavation site, and it looked for some time as if the space marines would be able to force a passage through to the plain under which the necron artefact was buried. However the sacrifice of the wraithknight led to a titanic detonation, killing or maiming many of the elite astartes troops and forcing the cancellation of the mission. The astartes withdrew, allowing the eldar to move up into the outskirts of Lochford. Instead of securing the device chamber for the imperium, the latest assault appeared to have poked a hornets nest which now threatened to remove the imperial presence from Corticant entirely.