Little & Eichman (2000), p. 250. It describes a Ming dynasty painting representing (among other figures) the Wudi: "In the foreground are the gods of the Five Directions, dressed as emperors of high antiquity, holding tablets of rank in front of them. [...] These gods are significant because they reflect the cosmic structure of the world, in which yin, yang and the Five Phases (Elements) are in balance. They predate religious Taoism, and may have originated as chthonic gods of the Neolithic period. Governing all directions (east, south, west, north and center), they correspond not only to the Five Elements, but to the seasons, the Five Sacred Peaks, the Five Planets, and zodiac symbols as well. [...]". Little, Stephen; Eichman, Shawn (2000). Taoism and the Arts of China. University of California Press. ISBN0520227859.
Espesset (2008), pp. 22–28. Espesset, Grégoire (2008), "Latter Han Mass Religious Movements and the Early Daoist Church", in Lagerwey, John; Kalinowski, Marc (eds.), Early Chinese Religion: Part One: Shang Through Han (1250 BC-220 AD), Leiden: Brill, pp. 1117–1158, ISBN978-9004168350. Consulted HAL-SHS version, pages 1–56.