In China 105 AD, the eunuch Cai Lun told his Emperor he had made paper. They had previously used bamboo and silk. The material used in this ancient paper included cotton rags, hemp, various plant fibres and old fish nets. The oldest existing paper with writing on it was found in the ruins of a watchtower in the Great Wall of China. It dates to about 150 AD. Even earlier paper (but with no writing on it) has been claimed: "The oldest surviving piece of paper in the world is made of hemp fibers, discovered in 1957 in a tomb near Xian, China, and dates from between the years 140 and 87 BC". Paper-making was regarded by the Chinese as so valuable that they kept it secret as long as they could.