Cursus of Alganar
Etched on the surface of the portal were figures resembling Humans but possessing a grace and beauty that is seemingly perverse. Possessing a curved black surface, the relic was almost half a mile long with Eldar images on its skin. Knowledge of its existence remained recorded within the Black Library of the Eldar.
During the Horus Heresy, the planet suffered from viral weapons deployed by the Iron Warriors Traitor Legion, during the Battle of Tallarn. In the aftermath, the world continued to thrive under the guidance of the Tallarn Desert Raiders of the Imperial Guard. Their excavations on their world led to them uncovering the ancient alien artefact. Following it being completely uncovered, the device activated with the dark, Eldar-like figures on its surface coming to life but seemingly twisted with an uncanny evil about them. Its activation became noticed by an Eldar of the Black Library who notified his Craftworld kin with the Farseers and Avatar of Khaine awakening as they recognised that their ancient enemy Slaanesh had a part to play in this incident.
This saw the Eldar strike Tallarn without warning as they lacked the time to explain their actions and did not know whether the natives were in league with Chaos or not. The goal was to destroy the Cursus before it could be fully activated and awakened from its endless slumber. The Imperial forces in the meantime retaliated, as they were ignorant of the true danger which allowed the portal to open, thus bringing Daemons into the mortal world that struck both sides. In the aftermath, the Human commander called a truce with the Eldar with their Seers recognising that alone they would lose this conflict. Furthermore, they came to realize that the Daemons weakened the further they went from the Cursus. Thus, hit-and-run tactics were employed with both sides working together against this common foe ultimately bringing about the defeat of the Daemonic horde with the Gateway closing as a result leading it to remain in a lifeless state.
In the aftermath, the Eldar and the Tallarns exchanged promises of friendship with one another. The Eldar provided mysterious devices to the Humans who placed them around the Cursus of Alganar that was reburied beneath the sands of Tallarn in order to prevent it from ever opening again as they were well aware that the ancient relic had once more entered into a slumber whilst it awaited the time till it could open once more.