Battle of Calth - Signs and Portents: There were many portents of the tragedy soon to unfold upon Calth. Given the extraordinary thoroughness with which the XIIIth Legion maintained its readiness, it might have been considered tragic, or incompetent, that so few were heeded. The first signs of the Word Bearers betrayal was the minor interruption in Vox traffic around Calth that was attributed to solar distortion -- the void was known to forever creak and whisper around the audible and electromagnetic ranges. Soon there were various reports of a voice chanting over Calthian Vox-links in Calth space. This eerie chanting soon interfered with the main orbital data-feed between the orbital installations and the surface of Calth for several seconds. An hour later, there were two more bursts of such interference, the source of which remained undetermined. Calth Communications Control reported an hour later that there were "a series of malfunction events" and warned that further communication disruptions might be expected during the day until the problem was identified. An hour after that, on the night side of Calth, the first of the bad dreams began.There were psychic portents as well. Hundreds of Ultramarines Battle-Brothers had been Librarians before the Emperor's decree at the Council of Nikaea banned the Space Marine Legions' use of psykers. Many Astartes Librarians of the Legions resented the Decrees of Nikaea, but honoured their oath to the Emperor and surrendered their Librarian panoply and wargear, returning to the lines as ordinary Battle-Brothers. Before the attack on Calth, those gifted with psychic abilities suffered severe headaches and pain behind the eyes. They ignored the pain, chalking it up to nothing more than fatigue after having gone without rest for several days during the preparation phase for the coming campaign against the Orks. It had not been possible to shut down higher mental functions and sleep, or at least remedially meditate. This mysterious pain was actually a warning sign broadcast through the Warp of the impending approach of the Forces of Chaos. The former Librarians all ignored the headaches. Few would survive the coming assault long enough to regret it.For days the Word Bearers' Chaos Cult echelons chanted monotonously into the ether as they conducted sacrificial rituals intended to bring forth the entities of the Warp to supplement the forces of the XVIIth Legion in the battle to come. Eight names were now repeatedly and constantly broadcast into the data flows of Calth's global Cogitator network. No data filter or noospheric barrier would block the repeating code or erase it, because it was only composed of regular characters. They were neither toxic code nor viral data, but once they were inside the system, and especially once they had been read and absorbed by the Mechanicus' noosphere, they began to grow in size. Soon these names became combinations of letters and then longer, deeper meanings essentially a form of runic Chaotic sorcery. These implanted meanings were caustic, infectious and indelible. There were eight of them, the sacred number of Chaos -- the Octed.At the orbital watchtower high above Calth, located at the Kalkas Fortalice, Uhl Kehal Hesst, a Mechanicus Server of Instrumentation, detected scrapcode within the global Cogitator system -- the dull amber threads of diseased information buried in the mass of healthy data. There was 2% more of it than any Analyticae projection had calculated for the Calth noosphere, the entirety of Cogitator data being used across Calth's global system, even under the irregular circumstances wrought by the conjunction of Imperial forces on the planet below. This was an unacceptable margin of error for the system, and the Mechanicus' senior Tech-priests reported the problem to Guilliman. They informed the Primarch that the scrapcode problem had been identified as a hindrance and that, though regrettable, these things did often happen within complex Cogitator systems and should not hamper his Legion's preparations for the coming campaign.