Aetheric Fields surround fortresses while they are vulnerable and protect them from aerial infiltration. Generated by the Aether Field Generator within the fortress, they are a shield that damages players who come within range. While effective at first, if the gates are breached, the generator can be destroyed causing the field to dissipate and opening the fortress to an aerial assault.
Historical Background Edit
Before the Epic Cataclysm a gigantic Aetheric Field defended the Tower of Eternity created by the Empyrean Lords. It was similar to the ones which defend the fortresses now, however the core of this field was formed by Aion himself. This made it unbelievably powerful; it withstood all of the Dragon Lords attacks combined with their Balaur Legions attack power.
Later on the Empyrean Lords used Aether to create a powerful barrier around the Tower of Eternity, protecting all of those within.