Chomsongdae, a 9.17 meter-high structure which belongs to the Old Shilla Dynasty. The observatory is located at Inwangdong, Kyongju City. On the retangular base stands the 27-layered tube-shaped body consisting of 362 blocks of granite. Between the 13th and the 15th layer on the southern side there is a small entrance, under which marks indicating a ladder hanging on it are still seen. The inside is filled with earth up to the 12th layer and stone bars are laid, at two points, between the 19th and 20th layer and between the 25th and the 26th layer. At the top are also two layers of stone bars in the same form, where the equipment for observation is believed to have been istalled. Chomsongdae, whose stone part has been preserved intact, is of great value not only because it is one of the oldest astronomical observatories of the world, but also because it is the oldest man-made structure in the orient. The exact year of its building is unknown, but according to Chronicles of the Three Kingdoms, it was built during the reign of Queen Sondok(632-646).