Quote Originally Posted by Cleretic View Post
It's actually never been 100% stated or clear what Louisoix did with the Twelve to try to stop Bahamut; the assumption of 'tried to summon the Twelve, failed' is a commonly-held one, but not actually confirmed, or even to the best of my knowledge stated at any point in-game.
Maybe not 100% a character absolutely stating it as a fact, but Gaius does mention it in-game in his (in)famous speech:
Are the "Twelve" otherwise engaged? I was given to understand they were your protectors. If you truly believe them your guardians, why do you not repeat the trick that served you so well at Carteneau, and call them down? They will answer--so long as you lavish them with crystals and gorge them on aether. Your gods are no different than those of the beasts--eikons every one. Accept but this, and you will see how Eorzea's faith is bleeding the land dry.
The aether he had left over from Louisoix's Twelve summoning attempt combined with the subconscious will of Eorzeans is also what made Phoenix IIRC and the lore book mentions that it has all the hallmarks of a primal summoning based on what we know. He was also potentially successful in partially summoning Althyk and that could explain how he sent 1.0 WoL 5 years into the future.

Out-of-game, the lore book directly describes Louisoix's attempt as a summoning.