At some point between the 6th century and the late 9th century, the entrance to the Barracks through Myrddin's Cave was locked with a mechanism that used a set of twelve Welsh artifacts as keys, known as the Treasures of Britain. The Treasures were hidden throughout the country of Britain and their locations were later encoded through clues written on tablets in verse pointing to the hiding places.
During the Viking expansion into England, the shieldmaiden Eivor Varinsdottir of the Raven Clan found all the tablets and unlocked the entrance to the Barracks, where she discovered the Sword of Eden Excalibur, which she claimed for herself.
Layla Hassan, an Assassin reliving Eivor's genetic memories in 2020, found two Isu inscriptions in the vault, one by Lug the Polymath and another by the Isu Mórrígan. Layla and the other Assassins in the same cell sent these images to linguist Antony Henry, who provided them with translations.
Shaun Hastings, who had been monitoring Layla's foray into Eivor's memories, proposed a theory that the Neolithic people discovered the Barracks and attempted to recreate the shape above ground, in the form of Stonehenge.