The Yungang Grottoes were carved during the Northern Wei Dynasty, under the charge of a Buddhist monk named Tan Yao, as ordered by the emperor. The grottoes extend one kilometre from east to west and consist of a series of 53 caves. There are 1,100 niches with about 51, 000 statues, the largest being 17 meters high and the smallest measuring two centimeters. Not only do the caves contain some of the oldest examples of stone sculpture to be seen in China, but one can see many foreign influences as well: Persian and Byzantine weapons, Greek tridents, and images of the Hindu gods Vishnu and Shiva. Bodhisattvas, dragons, and flying celestial beings represent the Chinese style. There are a number of Buddhist statues and decorative frescos in the Grottoes. One seventeen-meter Buddha with downcast eyes seems to gaze with penetrating insight into the human heart as it wavers between good and evil. An extremely rare statue of Shiva with eight arms and four heads is riding on a bull. Many of the carvings combine traditional Chinese art forms with foreign influences to create a unique style.