Construction of Cheomseongdae

Overview

Gyeongju Cheomseongdae (瞻星臺) is an astronomical observation structure built during the reign of Queen Seondeok of Silla, north of Wolseong in Gyeongju, near Gyerim and the tomb of King Naemul. The Samguk yusa, in the Record of Wonders section of the Gi-i chapter, states: "During this king's reign, dressed stones were used to build Cheomseongdae." The records disagree on its date: the Geographical Treatise of the Sejong sillok says it was built in the 7th year of the Zhenguan era of Emperor Taizong of Tang (633), while the Jeungbo munheon bigo says it was built in the 16th year of Queen Seondeok (647). It was designated a National Treasure in 1962.

Structure

According to the Encyclopedia of Korean Culture and Korean Wikipedia, Cheomseongdae consists of three main parts:

• Base: A two-tiered square foundation, measuring 5.36 m on each side at the bottom and 5.18 m at the top.
• Cylindrical body: Twenty-seven tiers of fan-shaped stones, each about 30 cm high, laid in the shape of a wine bottle. The body is 8.08 m high, about 16 m in circumference at the bottom, and about 9.2 m in circumference at the top. A square window about 95 cm on each side faces south at the 13th to 15th tiers. Below the window, the interior is filled with soil and rubble, while the upper part is hollow all the way to the top. At the 19th and 20th tiers and the 25th and 26th tiers, long stone slabs are laid in a "井" (well) pattern.
• Top section: Long stone slabs about 3 m in length are laid in two tiers in a "井" pattern.
• The total height is about 9.4 to 9.5 m. The number of stones depends on how they are counted. Some interpretations treat the 362 stones of the cylindrical body as corresponding to the number of days in a lunar year, but whether this matches exactly is unclear.

The dimensions recorded in the Geographical Treatise of the Sejong sillok (a height of 19 cheok 5 chon, an upper circumference of 21 cheok 6 chon, a lower circumference of 35 cheok 7 chon, and a hollow center through which people climbed up and down to observe) agree with the structure as it stands today.

Function

Astronomical observation in the ancient period had two aspects: observations for making and correcting calendars, and divination, in which changes in the stars were read to foresee good and bad fortune for the state. The Royal Chronicles section of the Samguk yusa states that the tomb of King Naemul lies southwest of the "Jeomseongdae" (占星臺, Star-Divination Platform), which shows that Cheomseongdae was also known by that name. The traditional interpretation holds that observers entered the interior by ladder through the window, stepped on the "井"-shaped stones inside, and climbed to the top to observe.