Persian Gardens refers to a tradition and style of garden design which originated in Persia (more commonly known today as Iran). Traditionally, such gardens would have been enclosed.
It is of note that the Persian word for "enclosed space" was pardeiza, which was inherited in Christian mythology as Paradise on earth, the garden of Eden. (see: Persians: Masters of Empire, p62, ISBN 0-8094-9104-4)
Its role was, and is, that of relaxation in a variety of manners: spiritual, and leisurely (such as meetings with friends), essentially a paradise on earth. The manner in which the garden is constructed maybe formal (with emphasis on structure) or casual (with emphasis on plant), and complies to various simple rules governing the design - this is said to allow a maximisation, in terms of function and emotion, of what may be done in the garden.
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The invasion of Persia by the Mongol Empire in the thirteenth century saw an emphasis on highly ornate structure within the Garden, examples of which include peonies and chrysanthemums. The Mongol empire then carried on a Persian Garden tradition in other parts of their empire (notably India). The Safavid Dynasty (seventeenth to eighteenth century) build and developed highly grandeur and epic layouts - which went beyond being a simple extension to a palace, and became an integral aesthetic and functional part of it.
http://en.wikipedia.org/wiki/Persian_gardens