Lore:Remnant of Argon
The Remnant of Argon is an Argonian artifact created by the Root-Whisper tribe of Argonians, in a last ditch effort to save both themselves and their Hist from the invading Barsaebic Ayleids. The invading Ayleids had been harvesting the souls of their tribe at an alarming rate, and so the Root-Whisper Hist sacrificed itself to create the Remnant of Argon, an amber artifact that could contain the souls of the entire tribe until the Ayleid incursion had passed. The Barsaebic Ayleids attempted to stop it's creation, but were held back long enough for the Remnant to be completed. 
Unfortunately, the Ayleids remained undefeated. Their leader, Myndhal, was driven mad in his quest for the Remnant, his attention having turned into an obsession with discovering whatever secrets the Hist had kept hidden from him. He and his mage, Houtern, created a network of portals all connected to a nexus realm in an attempt to either travel to wherever the now dormnant Hist had hidden the Remnant of Argon or to break directly through into the realm of the Hists. This continued for many years, and an undead Myndhal would eventually be encountered within one of the now countless portals by the Soulless One.
Meanwhile, though the Remnant of Argon was meant to only be a temporary measure, all knowledge of the Remnant was slowly lost to time. The Ayleid occupation lasted far longer than was anticipated thanks to Myndhal's obsession, and with the Root-Whisper Hist cut off from the rest of the Hists and the Root-Whisper tribe all but dead, there was no clear way for them to pass along the information of the Remnants location. Eventually, all knowledge the Remnant of Argon faded into obscurity, only remembered by the Hists and Argonians of Murkmire as something that invokes 'immense sadness'.
Eventually, a group of historians known as Cyrodilic Collections came to Murkmire on behalf of their Argonian benefactor to collect and preserve ancient Argonian relics. Though their benefactor, Kassandra, seemed to be altruistic motivations at first glance, she secretly hoped that one of the artifacts discovered could finally allow her to become connected to the Hist, something that had been an impossibility for her ever since her birth into Dunmeri servitude.
After Cyrodiilic Collections discovered both the origin of the Remnant of Argon and the Rootmender's Staff, which could lead them directly to the Remnant, Kassandra betrayed them, stealing the Staff and leaving the rest for dead.
Kassandra used the Rootmenders staff and a Vakka Stone to open a portal from the Nexus Realm directly to the hiding place of the Remnant of Argon, with the Soulless One and Famia Mercius giving chase. Kassandra successfully uncovered it and, claiming to finally hear the Hist, was promptly devoured by a Miregaunt. Thanks to her control over the Remnant, however, Kassandra had managed to take control of the Miregaunt and had to be defeated by the Soulless One. Famia picked up the Remnant and carried it to the safety of the now long-abandoned Root-Whisper Village. There, the Soulless One, the Bright-Throat Xukas, and the Naga Jaxsik-Orrn traveled into the Remnant of Argon itself in order to finally lead the lost Argonian souls out and reawaken the Root-Whisper Hist. In order to do this, one of them needed to stay behind and guide them back at the cost of their life, though it is unclear whether it was the Naga or Bright-Throat that did this. Regardless, because of their sacrifice, the Root-Whisper tribe was reborn, and the Remnant of Argon was finally no more.