http://www.mb-soft.com/believe/txo/zenbuddh.htm
The subsequent history of Ch'an in China was mixed. The sect suffered from the great persecution of Buddhism in 845. It recovered better than many Buddhist schools, however, partly because, in contrast to other monastic communities, Ch'an monks engaged in physical labor, which made them less dependent on state and lay support. During the Sung dynasty (960 - 1279), Ch'an again prospered and was a leading influence on the development of Chinese art and neo - Confucian culture.
It was during this period that Ch'an was first established in Japan. Within 30 years of each other, two Japanese monks, Eisai (1141 - 1215) and Dogen (1200 - 53), went to China, where they trained respectively in the Lin - chi (Japanese, Rinzai) and Ts'ao - tung (Japanese, Soto) schools of Ch'an. These they then introduced into Japan. Rinzai emphasizes the use of Koans, mental stumbling blocks or riddles that the meditator must solve to the satisfaction of his master. Soto lays more stress on seated meditation without conscious striving for a goal (zazen). Both schools fostered good relations with the shoguns and became closely associated with the Japanese military class. Rinzai in particular was highly influential during the Ashikaga period (1338 - 1573), when Zen played an important role in propagating neo - Confucianism and infusing its own unique spirit into Japanese art and culture.
The heart of Zen monasticism is the practice of meditation; it is this feature that has been most popular in Zen's spread to the West.
Zen meditation highlights the experience of enlightenment, or satori (Chinese: wu), and the possibility of attaining it in this life. The strict training of Zen monks, the daily physical chores, the constant wrestling with koans, the long hours of sitting in meditation, and the special intensive periods of practice (sesshin) are all directed toward this end.
At the same time, enlightenment is generally thought of as being sudden. The meditator needs to be jolted awake, and the only one who can do this is his Zen master. The master - disciple relationship often involves private interviews in which the Zen trait of unconventionality sometimes comes to the fore; the master will allow no refuge in the Buddha or the sutras but demands from his disciple a direct answer to his assigned koan. Conversely, the master may goad the disciple by remaining silent or compassionately help him out, but with the constant aim of trying to cause a breakthrough from conventional to absolute truth.