Time and its measurement have been preoccupations of mankind since the most primitive civilization in all parts of the world, and as his needs and his knowledge increased, so did man's awareness and concepts of time develop. In the Orient as in the Western World, the first timekeepers were such simple phenomena of nature as the sun, the moon, and the stars. The shadow cast by a tree or vertical object led to the invention of the sundial, and then the measured flow of water was discovered to provide another unit of time measure, as indeed did subsequently the flow of sand.