The Webway War

While Horus warred among the stars, a hidden and more terrible conflict raged beneath the Imperial Palace itself. The Emperor's grand project to master the Eldar Webway had been sabotaged from within by the fallen Magos Kelbor-Hal's allies, tearing open a breach through which the daemons of the Warp poured in an unending flood. This was the Webway War, and its front line lay a few miles beneath the throne room of Terra.

The Adeptus Custodes held the gate. Alongside the mute witch-hunters of the Sisters of Silence and the surviving loyalist Custodians, they fought a battle without glory or witnesses, sealing corridor after corridor against horrors that no mortal eye should behold. The Emperor Himself was chained to the Golden Throne, His psychic might the only bulwark keeping the breach from swallowing Terra whole.

Every moment the Emperor spent holding the Webway was a moment He could not spend directing the war against Horus. This was the cruel arithmetic of the age. When at last the gates were sealed, the cost was total: the Emperor could never again rise from His throne, and the great road between the stars was lost to humanity forever, its promise buried beneath the Palace like a tomb.