Hmm, what if Crystal Tower is where allagans are resting/ in stasis? That or its some type of teleportation device that transports people to the moon?

The Garleans have those dreadnoughts and we can assume that allagans had more advanced methods.

Whats also interesting is the Garleans converts aether into ceruleum to feul their magitek. Could they have started an astral era?