Before paper was invented, characters were carved on flat strips of bamboo or wood. Books made of bamboo or wood were heavy, and inconvenient for reading and carrying. In the Eastan Han Dynasty, Cai Lun used materials such as tree bark, hemp and rags to make paper, known as "Cai Lun Paper", Light and cheap, it soon became widespread and replaced bamboo and wood strips for writing, Later on, the technique of papermaking in China was introduced into countries around the world. As one of the Chinese Four Great Inventions, papermaking is considered to be a great contribution of the Chinese people to the world's civilization.