CheomSeongDae (瞻星臺) is a stone structure built in Gyeongju, the former Silla Dynasty capital, during the reign of Queen Seondeok (632~647AD). There exist dozens of hypotheses regarding its original purpose. Depending on to whom you ask, the answer could be a celestial observatory, a religious altar, a Buddhist stupa, a monumental tower symbolizing scientific knowledge, and so on. The most common perception of the structure among lay people is a stargazing tower. Historians, however, have suggested that it was intended as "a gateway to the heavens", specifically the Trāyastriṃśa or the second of the six heavens of Kāmadhātu located on the top of Mountain Sumeru. The name "Cheom-seong-dae" could be interpreted in many different ways. 'Cheom (瞻)' could refer to looking up, staring, or admiring, etc.; 'Seong (星)' could mean a star, heaven, night, etc.; and 'heaven' in that context can be a physical or religious reference. 'Dae (臺)' usually refers to a high platform on which people stand or things are placed. Researchers from the science fields often read 'cheom-seong' as 'looking at stars'; while historians read it as 'admiring the Trāyastriṃśa' or 'adoring Śakra'. Śakra is said to be the ruler of Trāyastriṃśa' who governs the Four Heavenly Kings in the Cāturmahārājika heaven, the first of the six heavens of Kāmadhātu. Śakra is the highest authority of the heavenly kings in direct contact with humankind. This paper examined the usages of 'cheom-seong' in Chinese literature dated prior to the publication of 『Samguk Yusa』, a late 13th century Korean Buddhist historical book that contains the oldest record of the structure among all extant historical texts. I found the oldest usage of cheom-seong (瞻星臺) in 『Ekottara Āgama』, a Buddhist script translated into Chinese in the late 4th century, and was surprised to learn that its meaning was 'looking up at the brightness left by Śakra'. I also found that 'cheom-seong' had been incorporated in various religious contexts, such as Hinduism, Confucianism, Buddhist, Christianism, and Taoism. In Buddhism, there was good, bad, and neutral cheom-seong. Good cheom-seong meant to look up to heaven in the practice of asceticism, reading the heavenly god's intentions, and achieving the mindfulness of Buddhism. Bad cheom-seong included all astrological fortunetelling activities performed outside the boundaries of Buddhism. Neutral cheom-seong is secular. It may help people to understand the nature of the physical world, but was considered to have little meaning unless relating to the spiritual world of Buddhism. Cheom-seong had been performed repetitively in the processes of constructing Buddhist temples in China. According to Buddhist scripts, Queen Māyā of Sakya, the birth mother of Gautama Buddha, died seven days after the birth of Buddha, and was reborn in the Trāyastriṃśa heaven. Buddha, before reaching nirvana, ascended from Jetavana to Trāyastriṃśa and spent three months together with his mother. Gautama Buddha then returned to the human world, stepping upon the stairs built by Viśvakarman, the deity of the creative power in Trāyastriṃśa. In later years, King Asoka built a stupa at the site where Buddha descended. Since then, people have believed that the stairway to the heavens appears at a Buddhist stupa. Carefully examining the paragraphic structure of 『Samguk Yusa』's records on Cheomseongdae, plus other historical records, the fact that the alignment between the tomb of Queen Seondeok and Cheomseongdae perfectly matches the sunrise direction at the winter solstice supports this paper's position that Chemseongdae, built in the early years of Queen SeonDeok's reign (632~647AD), was a gateway to the Trāyastriṃśa heaven, just like the stupa at the Daci Temple (慈恩寺) in China built in 654. The meaning of 'Cheom-seong-dae' thus turns out to be 'adoring Trāyastriṃśa stupa', not 'stargazing platform'.