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.

...

My soldiers returned a ragged volley of their own, save for the Watch. Throwing hooks above the fences, the Deoraithe found physical purchase and began to climb. I had hope, for a moment. Until the fences above the Proceran archers angled to drop the remaining stones harmlessly in front of the crusaders and disappeared. They shortly after reappeared above the fences keeping my skirmishers boxed in, cutting cleanly through ropes and hooks.

...

I knew better than to get my hopes up, and my pessimism was rewarded when the forward sides of the fences keeping my skirmishers contained winked out. They reappeared in a long diagonal in front of the advancing Broken Bells and my fingers clenched once more. Not a single of the knights died, but the length of the fence was unbreakable and forced them to take the long way around.

- Book 4, Chapter 14: Arabesque