The caisson has been found in tombs of the Han Dynasty dating the use of this architectural feature back at least 2,000 years. Besides subterranean structure, the oldest existent caisson in an above-ground structure is the one located above the statue of Guanyin in the Guanyin Pavilion of Dule Monastery, Jixian, Hebei province, built in 984 during the Liao Dynasty. Without the use of interior columns, this ceiling is held up by a hidden second-floor four-sided frame with a hexagonal ceiling frame on the third floor.