A little to the north of the Yenching University near Peking stand the ruins of the famous Yuan Ming Yuan. It was a palace built during the reign of Emperor K’ang Hsi of the Ch’ing Dynasty, about 200 years ago, and was given to and repaired and enlarged by Yung Cheng, his son. The Chinese unit of length at the time of building may have been different from the modern unit, and it is therefore interesting, mathematically and archaeologically, to determine the old unit by a mathematical method. Additional interest arises from the fact that the cut stones remaining belong to a section of the palace designed in Western style by Jesuit Fathers who came as missionaries to China. Did they use Chinese or French units in their plans?