In Khmer, Baray usually refers to a large rectangular-shaped lake with a temple called Mebon in the middle. The Baray and Mebon have multiple functions, as a water storage facility for agriculture and a religious site. The Baray was part of a royal tradition of the Angkor royals, whereby three royal gifts are endowed on a newly enthroned king; the Baray itself, a temple for the ancestors, and a state temple dedicated to the king’s reign. This concept seems to have developed during the reign of Jayavarman VII (AD 1181-1218). This is illustrated by urban planning design and the complex pattern of temples associated with Baray that were constructed during this period. Before the 13th century AD, the Mebon and Baray were separate entities, with the Mebon as secret places dedicated to the Hindu gods, rather than temples situated within lakes and ponds. But in the 13th century, and especially during the reign of King Jayavarman VII, they are strongly associated with Buddhism and placed in Baray. This poses the question, how and why did Javavarman VII, a Buddhist king, accept the concept of Mebon and Baray? To address the question, this presentation draws on the results of three excavations and surveys of temples constructed during the reign of Jayavarman VII: Srah Srang (excavated in 2021), the southern pond of Bayon temple (excavated in 2014), and Neak Pean (excavated in 2010). The results suggest the Jayavarman VII adapted the concept of the Mebon following the religious philosophy of Kāraṇḍavyūha Sūtra, which considers Avalokiteśvara a shiva in Buddhism. The archaeological research also provides evidence that both large Baray and small ponds could possess Mebon or the secret place in the centre, designed to symbolize purity and fruitfulness.