As it is an astronomical observatory of the Shilla Dynasty, which used to observe the movement of celestial bodies, it is about 9m tall with a wine bottle-shaped cylindrical part placed on the stylobate, which serves as a stand, and a pound button(井)-shaped top placed on top.The cylindrical part is made of fan-shaped stones stacked in 27 layers, and compared to the smooth and well-trimmed exterior, the interior has an uneven wall with jagged back roots of stones. Centering on the window facing southeast, the lower part is filled with pebbles, and the upper part is hollowed out to the top. At the top, where the eastern half is blocked with plate stones, the ends of long stones interlocked in the shape of a pound button (井) protrude all the way to the outside. This appearance is also found on the 19th to 20th and 25th to 26th steps, and it seems that it was suitable for hanging a ladder from the inside. According to an old record, it is said that “a person is supposed to go up in the middle”, and it seems that they placed a ladder on the outside, went inside through a window, and climbed up to the top using the ladder to observe the sky. Astronomy has a deep relationship with agriculture in that it can determine the farming season according to the movement of the sky, and it can also be seen that it is deeply related to politics, judging from the fact that astrology, which predicted the fortunes of a nation according to observation results, was regarded as important in ancient countries. Therefore, astronomy became a matter of national interest from an early age, and it is believed that this served as a good background for the construction of Cheomseongdae.It is presumed to have been built during the reign of Queen Seondeok of Silla (reign 632-647), and it is highly valued as the oldest astronomical observatory in the Orient, and is a valuable cultural heritage that shows the high level of science at the time.