In an attempt to rein in the excess of the upper classes, the Zen masters introduced the tea ceremony. In architecture this promoted the design of "chashitsu" (tea houses) to a modest size with simple detailing and materials. The style informed residential architecture with lighter, more intimate buildings relying on slender rafters and pillars with sliding inner partitions "fusuma" and outer sliding walls "shōji" . Although woven grass and straw "tatami" mats first began to appear in the Kamakura period, they were often thrown all over the floor. In the Muromachi period they began to have a regular size and be closely fitted together. A typically sized "Chashitsu" is 4 1/2 mats in size.