Origin of Roundtable Hold

This may be an easy question, but if it is, the answer is something I've missed on my first playthrough:

At what point, and under what circumstances, did the Roundtable Hold originate?

It is clearly closely bound to the state of the Erdtree, given the burning effects it shares when we burn the Erdtree. But I am not sure it is inside the Erdtree. It seems to exist in some extradimensional space that is removed from The Lands Between, but somehow still accessible to living beings.

It is highly likely that some extremely powerful force created Roundtable Hold, either intentionally or accidentally. In my mind, I think the most likely trigger for its creation was one of the following:

1. When Marika shattered the Elden Ring and the Tarnished were banished from the Lands Between. Marika knew that eventually a Tarnished would return to resolve the crisis, and as such saw fit to create a well-stocked safe haven for them, existing outside of time and space, and yet accessible via a maiden and the guidance of grace.

2. When the dragons attacked Leyndell. The presence of non-Tarnished entities in Roundtable Hold may be explained by those beings being rushed to the Fortified Manor during the dragon assault and then whisked away by Marika for safety. Alternately, if Gransax had any of the time and reality-warping powers as Placidusax, then he may have accidentally created a timeless extradimensional space when attempting to attack the Fortified Manor, where the Two Fingers were hiding.

I am more inclined to think that the space was carefully planned and curated by Marika given the special instructions and task left to Hewg. But if there is any dialog or description that goes into detail on its origin, I have missed it.

Extra credit if anyone knows who or what the Twin Maiden Husks are/were.