Ahead of the retreating Watch, panes of light bloomed. At least forty feet tall, though thin. A fence, I realized. They are fencing them in. Pane after pane formed, boxing in our retreating skirmishers in the span of time it’d take me to light a pipe. An opening was left, at the back. Where the enemy bowmen paused and put their formation in order, as on both sides of them the Proceran cavalry began to charge.

“Tell Pickler to fire at will,” Juniper barked at the closest mage.

The message passed and the twenty heavy ballistas fired their stones. The first volley hit the fence at a high angle, and the stones broke without even visibly affecting it. The trebuchets threw their load in the moment that followed, arcing high over the fence straight at the enemy archers. They never reached the crusaders. More fences formed over their heads. Some rocks shattered, others bounced off. The broken remnants remained on the light, as if it were a physical thing. I gestured for another mage to attend me.

- Book 4, Chapter 14: Arabesque