Most of the Yün-kang 雲岡 Caves were carved out during the period when the Northern Wei 北魏 Dynasty ruled from P’ing-ch’êng 平城. The oldest of all are the ones known as “The Five Caves of T’an-yao 曇曜五窟¨, which were planned as early as the Hê-p’ing 和平 era (A. D. 460-465) by T’an-yao 曇曜, whose title was Sha-mên-t’ung 沙門統 (administrator of monks). The main Buddhist statues in these five caves (Caves XVI-XX, according to the present classification) were gigantic in scale, bigger than any others in China at that time. The Chapters on Buddhism and Taoism 釈老志 in the Wei-shu 魏書 tell us that the five caves were excavated for the first five emperors of the Northern Wei Dynasty, (T’ai-tsu, Tao-wu-ti 太祖道武帝; T’ai-tsung, Ming-yüan-ti 太宗明元帝; Shih-tsu, T’ai-wu-ti 世祖太武帝; Kung-tsung, Ching-mu-ti 恭宗景穆帝; and Kao-tsung, Wen-ch’ing-ti 高宗文成帝). Furthermore, we are told, the features of the statues were carved to resemble the five emperors. The practice of honoring emperors by carving out stone-caves and placing statues of Buddha inside was continued even after the Northern Wei Dynasty moved to Lo-yang 洛陽, as is evidenced by the Lung-mên 竜門 and Kung-hsien 鞏県 Caves. The practice was followed, in fact, until the fall of the dynasty.In the case of “The Five Caves”, the author takes special notice of the fact that the statue placed in Cave XVII is an image of Maitreya Bodhisattva with ankles crossed. The statues in the other four caves are of Śākyamuni Buddha (two standing and two seated). This raises the question of why T’an-yao made only one out of five statues in the image of Bodhisattva with ankles crossed. In addressing himself to this question, the author considers the following factors:1. The shapes of Buddhist statues.2. The political situation (especially the persecution and restoration of Buddhism) during the time the Yün-Kang Caves were carved out.3. The characteristics of Liang-chou Buddhism 涼州仏教 as a religion.4. The relationship between Taoism and Buddhism.The author reaches the following conclusions: T’an-yao 曇曜 saw the successive emperors of the Northern 'Wei Dynasty as “past Buddha—present Buddha—future Buddha”, and claimed that “the Emperor is Buddha Himself.” Dead emperors were represented by statues of Śākyamuni Buddha while the then reigning emperor was Maitreya Bodhisattva. In the Northern Wei Dynasty, the present emperor was represented to the common people as a Messiah (Savior) who descended upon the earth as Maitreya to save mankind. Buddhism thus came to be regarded as the state religion of the Northern Wei Dynasty.