蔡伦
Scrolls in bamboo strips, mostly for text, were referred to as "pian" (篇), while those in woven silk, mostly for large pictorial representations, as "juan" (卷); both are called scrolls because they were rolled up, bound, and tagged for identification. The practice of using scroll pouches called "ji" (帙) to hold five to ten scrolls had been in existence ("Shuowen Jiezi" defines the character as "book clothes"), but paper had not been invented by Cai Lun until 13 years after Ban Gu's death. The earliest form of back-bone binding of books, the butterfly binding (蝴蝶裝), was not invented until around 1000.