A long time ago

As it was revealed from the journalists' visit on the set, there will be quite a few flashbacks in Justice League. One of them concerns the history of the Mother Boxes. And one of these Mother Boxes is in Atlantis.

As expected, it was brought there before the continent was submerged. And we do see in the Justice League teaser trailer how one Mother Box is buried by what seem to be the Ancient Kings of Atlantis.

One rumor suggests that we see the Dead King, one of Aquaman's foes, burying the Mother Box. If this is so, maybe we have already found out how the Aquaman solo flick will go "“ Atlan returning in order to reign again over the continent.