Aurum (Planet) - Grensvayl: Some one hundred and fifty kilometres from Haistand, the town of Grensvayl was once no different from the hundreds of other agricultural settlements that dot Aurum's fertile mesas. The town was built where the Espri River splits into 3 branches, providing natural irrigation to a large orchard on the eastern edge of the town.Indeed, there was once a time when the Commerce Aisles of Haistand spilled over with red pears and handfruit from the Grensvayl orchard.Then the Hereteks of Samech came to plunder Aurum's Decavane Crystals. The Dark Mechanicum of the Jericho Reach's most infamous Forge World have a fascination with xenos specimens. Over a solar decade ago, they brought several Genestealers with them as tools of misdirection and destruction.Their plan had both a short term and a long term goal. For the first few solar years of the heretical machine cult's occupation, the Genestealers did what they were born to do: destabilise and thin the enemy ranks.Their nightly depredations created such an atmosphere of paranoia that a few strange noises or lights from the cliffs seemed just another eerie mystery. Certainly with rumours of lurking monsters, the inhabitants felt little desire to poke around in dark caves.In the long run, the Dark Mechanicum hoped that the infection would spread, leading Hive Fleet Dagon to Aurum and denying this prize world to the Imperium. This fate could still come to pass.Their scheme went smoothly -- at first. The dark magi did not count on the Caele being so quick to react to the odd behaviour of Grensvayl's population. After several unsuccessful attempts to cleanse the settlement, Rylus instituted the fiery quarantine which has stood to this day.While not their ideal outcome, this served the dark magi well enough, as it allowed them to continue their mining unhindered. However, as the years marched on, the number of Purestrain Genestealers increased and the supply of other living beings diminished.Like most Tyranid organisms, Genestealers can subsist on nearly any type of biomatter, but their instincts drive them to hunt animal prey first. The creatures grew ever more predatory and clever as they grew more desperate.Eventually they found a way into the mining caverns, putting a bloody and premature end to the Decavane Crystal collection.Below are some of the most prominent attempts made by the Genestealer Cult to break out into the wider population of Aurum prior to Grensvayl's destruction:806.M41 - Only a few solar months after the Caele sealed off the ravine, a group of infected warriors found an opening where the river used to flow out through underground channels. Fortunately a perimeter sentry spotted the infected warriors as they started to cross the plains. The sentries were able to put the hideous beings down, but at a great loss of life. They promptly sealed the egress points of all three river forks as well.810.M41 - The first sizeable generation of Purestrain Genestealers matured in this period. One night they made a coordinated push through the fire perimeter. Though badly injured, the creatures still nearly overwhelmed the sentries. Only a few Auran warriors survived the bloody night.815.M41 - One of the xenos, possibly the Genestealer Patriarch, had grown in power and cunning over the years. It manifested psychic powers and managed to mesmerise one of the sentries into letting it pass through the barrier. Fortunately other warriors witnessed its escape and managed to bring it down.817.M41 - Karthas persuades Rylus Darkscourge to attempt an extermination of the "Malissectors" of Grensvayl one last time. He leads a war party into Grensvayl with disastrous results. Later that same solar year, a Deathwatch Kill-team finishes what he started, wiping Grensvayl off the face of Aurum.