The koloss army was another thing that got shuffled about in this book. Originally, the Luthadel folks discovered its advance pretty early on. All of their discussions, then, talked about the fact that they had three armies bearing down on them.
I pushed back knowledge of the koloss for a couple of reasons. First off, koloss are scary—and I think they deserve to be treated differently from the other two armies. Their appearance can throw a real wrench into things later on, once Elend and company hear about them. It allows for the reader to know something that most of the characters do not, and leads to anticipation and tension.
In addition, it gives Sazed another good reason to exist in the plot. Now he knows about the koloss and nobody else inside the city does. His mission, therefore, is even more vital. He has to bring information back to his friends.
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