Silk is a kind of fabric made of fibers from the cocoon of the silkworm. Natural or 'raw' silk is produced from silkworm cocoons in a process known as sericulture; the caterpillars are killed in the process. Many modern silks are synthetic, and no caterpillars are involved in their manufacture.
Silk was first developed in early China, possibly as early as 6000 BC and definitely by 3000 BC. Though first reserved for the Emperors of China, its use spread gradually through Chinese culture both geographically and socially. From there, silken garments began to reach regions throughout Asia. Silk rapidly became a popular luxury fabric in the many areas accessible to Chinese merchants, because of its texture and lustre. Because of the high demand for the fabric, silk was one of the staples of international trade prior to industrialization.
Perhaps the first evidence of the silk trade is that of an Egyptian mummy of 1070 BC. In subsequent centuries, the silk trade reached as far as Europe, the Indian subcontinent, the Middle East, and North Africa with traders. So extensive was this trade that the major set of trade routes between Europe and Asia was known as the Silk Road.
The Emperors of China strove to keep the knowledge of sericulture secret from other nations, in order to maintain the Chinese monopoly on its production. This effort at secrecy had mixed success. Sericulture reached Korea around 200 BC with Chinese settlers; by 300 A.D. the practice had been established in India. Although the Roman Empire knew of and traded in silk, the secret was only to reach Europe around A.D. 550, via the Empire of Byzantium.