NCsoft began trial testing for rifting events in Aion last December and it seems that the players liked what they experienced, so NCsoft is bringing it back for several more months. Starting April 13th, Aion players can join the "Behind Enemy Lines" event set to take place every other week, allowing players to enjoy its benefits one week and remove them the next.

The first week of the event will run from April 13th through April 20th to allow players to experience more of Aion's content. During the rifting event, the defensive buffs in Heiron and Beluslan will be removed, but Eltnen and Morheim will still have their defensive buffs in place during the event.

Source: Aion website