In the little plaza at the junction of the Power House and Riding Hall, the road winds and passes under the mediæval arch of the Post Headquarters, or Administration Building. At this point, the bulk and dignity of the buildings are stupendous, and admiringly we stand, imprisoned, it would seem, in a quadrangle of Middle Age fortresses, whose sternness and solemnity seem symbolic of discipline and strength. The main entrance to the Riding Hall branches from the road a few paces beyond the arch, the lower level of the galleries being reached by a flight of steps that cling to the steep retaining wall of the road. The great arena is 150 by 600 feet and is covered by a cantilever roof, so that when the eye first encounters this interior, a sensation of its vastness holds the spectator in its grip. The roof is mostly of glass so as to afford a maximum of light, and the floor is covered with tanbark to make more endurable any sudden and unexpected descent from the back of a capricious beast. The building is steam-heated and electric lighted, for during the winter months, equitation drills extend into the late afternoon. The hall can be divided by curtains into three smaller halls, a scheme that permits three classes to undergo instruction at the same time. In one portion of the hall are stalls for one hundred mounts, but the majority of the horses are kept at the cavalry barracks. The hall is so large that during the winter months the U. S. M. A. Battery of Artillery uses it for a drill ground, thereby keeping the horses in good condition and the men well instructed. Moreover, the officers and cadets are enabled to keep up their practice in polo. Every Wednesday and Saturday afternoon, teams of cadets play each other, or try their skill against civilian opponents. Along the full length of the west wall, and the north and south end, are balconies for the accommodation of visitors who are welcome whenever the hall is open. [Illustration: Administration Building Riding Hall]