Final answer:
The Bayon Temple is the major Khmer monument associated with Buddhism, built as the state temple at Angkor Thom during the 13th century.
Step-by-step explanation:
The major Khmer monument associated with Buddhism is the Bayon Temple. Constructed in the 13th century, the Bayon Temple was built at the center of Angkor Thom, the capital city of the Khmer Empire. It served as a state temple and a monument to Buddhist cosmology, featuring numerous serene and smiling stone faces on its many towers that gaze outwards in all directions, symbolizing the omnipresence of the bodhisattva Avalokiteshvara. Despite the Hindu origins of many Khmer monuments, such as Angkor Wat which was originally dedicated to the Hindu god Vishnu, the Bayon Temple reflects the Mahayana Buddhist beliefs that became prominent during the reign of King Jayavarman VII.