Selection and subsequent placement of rocks was and still is a central concept in creating an aesthetically pleasing garden by the Japanese. During the Heian period, the concept of placing stones as symbolic representations of islands – whether physically existent or nonexistent – began to take hold, and can be seen in the Japanese word "shima", which is of "particular importance ... because the word contained the meaning 'island Furthermore, the principle of "kowan ni shitagau", or "obeying (or following) the request of an object", was, and still is, a guiding principle of Japanese rock design that suggests "the arrangement of rocks be dictated by their innate characteristics". The specific placement of stones in Japanese gardens to symbolically represent islands (and later to include mountains), is found to be an aesthetically pleasing property of traditional Japanese gardens.