When the Chinese discovered the secret to creating silk, they held the monopoly on silk production worldwide. The industry was such a boon to Chinese trade that an imperial decree was issued which condemned to death anyone who attempted to sneak silkworms or eggs out of the empire.
But the secret did eventually get out, and there are lots of theories concerning how. One tells the story of a Chinese princess who was wed to the Prince of Khotan. She loved silk so dearly that she hid silkworm eggs in her hairpiece. However, Khotan also kept the secret, so the mystery of silk continued for the westerners. By 300 CE Japan learned the secrets of silk production when a Japanese expedition managed to take some silkworm eggs and also four young girls who were trained in the art of creating the material.
The West finally cracked the secret in 552 CE when the Byzantine emperor Justinian sent two Nestorian monks to central Asia. The monks hit the eggs in their hollow bamboo staves. The eggs hatched into worms which then spun cocoons. Slowly but surely silk production began to spread around the world, and the Chinese re-established themselves as a major silk supplier.