- "The defenders of Earth made a vow - Men, Atlanteans, and Amazons. Each would enshrine and guard the three sleeping Motherboxes according to the rites and rituals of their culture in case a box should ever wake again to call out to the planet Apokolips to return and conquer the only world Darkseid had ever lost."
- ―Wonder Woman[src]
A stronghold located on the perimeter of the Kingdom of Atlantis was used to store a Motherbox claimed from Darkseid by Atlan and the Unity of Earth following the Battle for Earth. Thousands of years later, long after Atlantis sunk into the oceans, the Motherboxes sensed the death of Superman and was reactivated, waking from its slumber and calling to Steppenwolf, who reclaimed it from the Atlanteans' outpost in his conquest of the world to complete the Unity.
In his youth, Uxas of Apokolips arrived at Earth with an armada during his search for the Anti-Life Equation. After discovering the Equation in the crust of the planet, Uxas and his forces engaged the but were defeated by the combined strength of the Old Gods, Green Lantern Yalan Gur, and the armies of the Amazons, Humans, and Atlanteans. King Atlan formed an agreement with Queen Hippolyta of the Amazons and the leaders of Men to guard the boxes and unite once more should they awake again. Atlan and his soldiers placed their Mother Box within a stronghold on the outskirts of Atlantis, establishing a constant guard around the device, where it remained dormant for centuries.
Thousands of years after Atlantis sunk into the oceans, the Atlanteans remained true to their vow and continued to guard the Mother Box in the modern age. Mera was guarding the stronghold when the box was awoken by the cries of Superman in his death at the hands of Doomsday, witnessing the box surge with power before falling dormant again. Months later, after reports of missing guards at the stronghold did not sway King Orm to send reinforcements to the outpost, Mera was present when a boom tube opened beside the Motherbox and was attacked by Steppenwolf. Using her sorcery, Mera engaged the invader, expanding the surrounding water to cause him to fall deeper within the outpost before collapsing it back onto him.
Quickly recovering, Steppenwolf seized Mera by the throat and told her she couldn't escape him, but she replied that she wasn't trying to before using her hydrokinetic abilities to draw all the fluid from the New God's body, including his blood, but was tossed into a walkway before she could kill the creature. Charging, Steppenwolf swung his Electro Axe at the Atlantean's neck but was intercepted by Aquaman, who attempted to defend the Motherbox but was dazed by Steppenwolf long enough for him to obtain the box and retreat through a boom tube back to his base.
In the aftermath of the attack, Mera spoke with Arthur, explaining that Nuidis Vulko told her he would come to help them defend against the invaders. Mera warned him that it would've been the task of his mother, Queen Atlanna, to follow Steppenwolf to the surface and defeat him, but it was now his responsibility as the first born son of the queen.
- Many believed that the stronghold was located in Atlantis. However, in Aquaman, Arthur Curry mentions several times throughout the film, he had never been in Atlantis before, which confirms that the vault is in another location. Director James Wan explains. "It wasn’t Atlantis. I spoke with Zack Snyder, early on, and Zack mentioned that the location that Aquaman swims to in “Justice League” is an outpost. So when he told me that was his idea, I was like, 'Oh great, then I can actually have Arthur go to Atlantis for the first time.' That's very important for me, because he can go into it and have a wide-eyed approach to Atlantis and be in awe of it. I think that's very important from a storytelling standpoint because the audience gets to experience Atlantis for the first time along with the character." Furthermore Wonder Woman states that a Mother Box was "entrusted to the Atlanteans", who kept it "sealed and guarded in a secure stronghold". Nowhere is it mentioned that the mother box is actually kept in Atlantis itself.
- In Justice League concept art, the Vault was originally guarded by the Fishermen.