In the Immortal Flames Quest there is: Like Father, Like Son where Cid and Darnus have a talk in Tomb of the King of Allag in Mor Dhona..

Cid said this:
"Bozja Citadel... An entire city gone in the blink of an eye. All the literature left to us of Allag, the lunar transmitter, the testing facilities-all gone without a trace. not a page or stone remained. Nor even a corpse."
Like you can read seems even 10 years ago Garleans used a transmitter.. but Bozja destroyed in only one night :|
Or maybe they had the transmitter but they hadn't used, and tried the ancient spell Meteor...
Surely every information and machina left from Allag seems was in Bozja Citadel, and now seems lost forever, But always in "like father, like son" Darnus ask to Cid to tell him the secrets of Allag.. Meteor..

Cid: "So you've found me. And what now, Raven?"

Darnus: "Ah, but you already know full well. You know Garlemald seeks to save this world-to cleanse it of the eikons' taint." "And you also know that to do so we require the ancient secrets of Allag. Secrets said to have died with that Empire long ago-secrets of which you know quite a deal." "So come, Master Cid, and tell me what it is I wish to know."

Cid: "The secrets of Allag..." "Meteor... You truly mean to do it, then? To bring down Dalamud?"

Darnus: "How shrewd. Good. You will save us much time. Long have we sought to rediscover knowledge of the Meteor sorcery. For years it was Midas nan Garlond who led our efforts. You father was both a genius and a patriot."

Cid: "I know who my father was-just as I know he was killed serving Garlemald's blind ambitions."
So, Cid know the secrets of Meteor..

I think that night, 10 years ago, they don't bring down Dalamud (of course) but awake Bahamut give to him a lot of Aether, but Dalamud was too far to control where Flare hits (or maybe Bahamut hits where the aether's source is, like now in Mor Dhona), and Bahamut hits with Flare over Bozja, destroying everything in one shot..
The only question is: How Bahamut can cast Flare from the inside of his prison? Dalamud haven't this purpose? Prevent the power of Bahamut?

But the real question has pounding me is: Garleans know Bahamut was inside Dalamud?? Reading recent quest text and cutscenes dialogue seems Darnus and Baelsar know something was inside... So, Why use an Eikon to destroy the Eikons?? This not be more wicked?

PS. Sorry for my confusing english