On the basis of books and maps about the military f ortresses of the Great Wall in the Ming Dynasty, GI S-based cost-surface and the best path are calculated and t he road map of the military settlement of Xuanfu to wn is drawn to restore the space layout, traffic network and commu nication station of military settlement. Restoring ancient roads with GIS is proved to be feasible. This paper analy zes the defense mechanisms of the Xuanfu town accor ding to the road map.