It seems that the Chomsongdae at Kyongju is involved in not only a function for astronomical observation but also various symbolic functions. We can easily find many interesting features, even if we simply consider it an observatory. (1) If we assume that the latitude of its location is driven from(90° - Tan⁻¹(41/9) + 23° 27′), the real location is far only 5 seconds. Tan⁻¹(41/9) is the altitude of sun in the summer solstice: the ratio of 41 pole height to 9 shadow length can lead us tI the ratio from 9:40:41 rectangular triangle. Moreover, 9 is a symbolic number in the Orient, and Tan⁻¹(41/9) or Tan⁻¹(9/41) is mysterious angle too, but it will be left aside here. (2) The diagonal of the low square base denotes the direction of sunrise in the winter solstice, and we can find that there are four important tombs in the production of that line. These are symbolic, too. (3) The generatrix on the surface of revolution shows sine curve that vertically represents a half period of the ecliptic curve from its bottom to 24 horizontal layers of granite blocks. It can be regarded that the purpose of its curve is based on the observation concerning the altitude of sun at noon by which the coordination of the generatrix vertically transfers to the top. (4) There are double parallel crosses at stone bars on top, and they correspond with the direction of sunrise and sunset every solstice and equinox, or the position of Alkid in the big Dipper per hour in the particular position of them. It means that one could recognize time at night and the differentiation of season. (5) The shadow of the stone bars indicates a time at noon every solstice and equinox on the surface of revolution, so it may be served one of the landmarks for the people. Thus, Chomsongdae has many meanings, and when we interpret them on the basis of ancient principle, we should attach importance to the Book of Changes. For example, we can find the solution by integral numbers regarding the Pythagorean theorem among them, and Chomsongdae might be applied to them. Finally, Chomsongdae comprises 27 layers of stone blocks, and the surface of revolution. It connotes the following relation: 365² = 364² + 27². The figure 27 means the number of the order of Queen Sondok, 365 the number of the days in one year.