Ambush

"Hold your ground. Let them engage the defenses first." Aleyria instructed her soldiers comprising half of the King's Guard and the two thousand members of the Royal Dragon Battalion and the Royal Phoenix Battalion. 

They were hiding in a small forest two kilometers away from the Western Main which Isabella had created with her incredible Verdant magic. It was a very simple ambush, really. So simple that it bordered on stupidity. 

They were simply lying in wait in two patches of trees and allowing the enemy to attack partially rebuilt walls of the City of Rin. Alexander had instructed them to station one battlecruiser there and have it switch on its engines on and off, as though it was struggling to power up. Station the mothership behind it and have its engines fully turned off. Then, surround the battlecruiser with a bunch of defensive mages and release their auras to the full.