Introduction to river dams in the Northern Wei Dynasty: There was originally Wuzhou River in front of Wuzhou Mountain, about 25-50 meters north of the grottoes. In the Later Jin Dynasty, in order to prevent water from corroding the grottoes, the river course was moved southward, and the ruins of the river dam are now left. In 1993, during the archaeological excavation of the Yungang Grottoes site, a stone dam was cleared in front of Cave 20. When the water pipes were dug and buried in Yungang Square in 2003, the bottom was covered with cobblestones. Physical evidence proved that the original Wuzhou River water flowed in front of the Grotto Temple.