Before the invention of paper, ancient civilizations used various materials for writing: the Egyptians used papyrus, the Mesopotamians used clay, and the Chinese used bamboo strips or silk. In 105 CE, a court official named Cai Lun revolutionized communication by inventing the papermaking process. He used a mixture of mulberry bark, hemp, old rags, and fishnets, which were mashed into a pulp and dried in thin sheets. This new material was lightweight, cheap to produce, and easier to store than bulky bamboo or expensive silk. Paper allowed for the mass production of books and the expansion of the Chinese bureaucracy. The secret of papermaking was closely guarded for centuries until it reached the Islamic world in the 8th century through prisoners of war, and eventually reached Europe via Spain. It is considered one of the 'Four Great Inventions' of Ancient China that changed the course of global history.