The construction of Cheomseongdae in 647 AD marks the establishment of East Asia's oldest surviving astronomical observatory in Geumseong (present-day Gyeongju), the capital of Silla, during the late reign of Queen Seondeok, Silla's 27th monarch. This period was fraught with external threats from Goguryeo and Baekje, demanding national unity and strength. Queen Seondeok herself faced internal strife, such as Bidam's rebellion. Amidst these challenges, the Queen actively promoted science, technology, and culture to stabilize the populace and strengthen royal authority, with Cheomseongdae being a pinnacle of these efforts. In ancient societies, astronomical observation was crucial for agricultural planning and for legitimizing royal power through divination and the interpretation of celestial phenomena. Cheomseongdae is a unique stone structure, approximately 9.17 meters tall, composed of a base, a cylindrical body, and a square top. Its most distinctive feature is the 27 layers of stones forming the main body, widely interpreted to symbolize Queen Seondeok as the 27th ruler of Silla. The total number of stones used, 362, is believed to represent the number of days in a lunar year, showcasing the sophisticated cosmological understanding and mathematical knowledge of the Silla people. The structure's circular body atop a square base and capped with a square top embodies the ancient East Asian concept of "round heaven and square earth" (Cheonwonjibang). Lacking internal stairs, observers likely used a ladder to reach the top for celestial observations. Cheomseongdae is not merely an observational facility but a masterpiece that encapsulates Silla's advanced stone masonry techniques and architectural aesthetics. The construction of Cheomseongdae stands as a testament to the highly advanced scientific and technological capabilities of Silla. Its significance is further amplified by its status as the oldest extant astronomical observatory in East Asia. It served crucial political and social functions by enabling the prediction of astronomical events for agricultural prosperity, interpreting omens to bolster the legitimacy of royal power, and fostering national cohesion among the populace. Queen Seondeok intended Cheomseongdae to showcase her governance capabilities and Silla's cultural excellence both domestically and internationally. Today, Cheomseongdae is part of the Gyeongju Historic Areas, a UNESCO World Heritage site, and remains a prominent cultural heritage symbolizing Silla's thousand-year history and scientific spirit, fostering a sense of pride among Koreans.