The magic of Recluce - L. E. Modesitt

For centuries the Masters of Recluce have guarded the borders of their
Order-wrought land and destroyed every threat sent against them.
But the power that defends the people of Recluce comes at a cost:
absolute obedience to both the Masters and the rule of Order. And those who cannot abide the price of paradise are swiftly dealt with ...
So when a young man, Lerris, becomes bored with the simple, orderly life of Recluce, he is sent into exile. For Lerris it is a chance for adventure, for the Masters it is a way to make him see the error of his ways.
But there are other powers in the world than Order. And when the great Chaos-Master Antonin learns of Lerris' exile he sees in it a way to break the Master's rule and bring about the destruction of Recluce ...

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