Wait a minute...is this a plot-hole (Austerities of Wind and Main Scenario-related)?

[Bfmusashi]

I don't recall the time period for the Summoners original existence, but it was likely while the ability to summon the primals was sealed at Silvertear Falls. I think this is the only seal you can put on them, that they can't be properly summoned, but their calmer, smaller representatives can. So, having the big manifestation trapped and locked in the Ultima Weapon/Silvertear Falls doesn't seem to keep the less willful versions from manifesting.

[WyrahFhurrst]

I don't recall the time period for the Summoners original existence, but it was likely while the ability to summon the primals was sealed at Silvertear Falls. I think this is the only seal you can put on them, that they can't be properly summoned, but their calmer, smaller representatives can. So, having the big manifestation trapped and locked in the Ultima Weapon/Silvertear Falls doesn't seem to keep the less willful versions from manifesting.

Summoners were created by the Allagans, so the Third Astral Era. And I'm not sure there ever was a "seal" on the Falls, just that when the Agrius exploded it released a great amount of aether into the world. Without enough aether to summon a primal, no Egi would have been summoned, because one must defeat a primal in the first place in order to summon an Egi.