Sundering and specific character questions. [Spoilers]

[Vyrerus]

The thing that makes me question when the moon came into being are the buildings we see at Mare Lamentorum.

Perhaps Hydaelyn's summoners created it originally as a safe haven in case the Final Days returned and ended up completely destroying the world, but had it used as Zodiark's prison further down the line?

I think it's pretty much a research outpost turned memorial. If the Ancients were as invested in studying and stewarding the planet as Emet-selch says, then it makes sense that they'd want a full view of their planet. I actually kind of wonder if there was more than one moon before.

Of course, I can't help but think of our own moon's incidental function... it soaks up many many meteors, asteroids, and other celestial bodies that would otherwise touch down on Earth. Both small and large. Hence why it's covered in craters.

Perhaps the moon with Mare Lamentorum was made after the Final Days, but before Hydaelyn's creation. Perhaps as both a planetary observatory, and a meteor aegis.