Causes of Appearance of Iran's Historical Gardens

In the wide territory of Iran, there are gardens that are considered as valuable examples, from the point of view of art and architecture and popularized Iranian landscape design in other countries and especially in Islamic ones. Many books and papers were written about these gardens but not much talk about the reasons of appearance of the gardens that were mostly in hot and dry continents. Was the only purpose of design of these beautiful gardens, just a shelter from the heat? Are gardens, symbol of thoughts of their period? What were the reasons to build these masterpieces of landscape architecture? We can say that governor’s thoughts in different time periods strongly influenced every aspect of architecture, including garden design. Elements such as religion, recreation, government and politics were the main causes of these designs.