The Chinese introduced gardens to Japan in the 6th century. As a result, the earliest Japanese gardens displayed a strong Chinese and Buddhist influence, as Buddhism was very popular in China at the time (and still is today). Paradise gardens are crafted to emulate the Buddhist notion of the Pure Land -- a sort of heaven before enlightenment. Partly due to the civil unrest during this period, the Japanese eagerly embraced the idea of the Pure Land, and these gardens became very popular.
The typical paradise garden has an island in the middle of a pond to represent future salvation. A curved bridge connects the island to the rest of the garden to represent the path one must travel to reach that salvation. Although few original paradise gardens remain, many present-day Japanese pavilions are modeled after the buildings that once graced their grounds.