SeeThe 7 Wonders of the World :2 The Hanging Gardens of Babylon

The Hanging Gardens of Babylon, one of the Seven Wonders of the Ancient World, is the only one whose location has not been definitively established. The Hanging Gardens were a distinctive feature of ancient Babylon. They were a great source of pride to the people. Possibly built by King Nebuchadnezzar II in 600 BC, the gardens are believed to have been a remarkable feat of  engineering: an ascending series of tiered gardens containing all manner of trees, shrubs, and vines. The gardens were said to have looked like a large green mountain constructed of mud bricks.

Traditionally they were said to have been built in the ancient city of Babylon, near present-day Hillah, Babil province, in Iraq. The Babylonian priest Berossus, writing in about 290 BC and quoted later by Josephus, attributed the gardens to the Neo-Babylonian king Nebuchadnezzar II, who ruled between 605 and 562 BC. There are no extant Babylonian texts which mention the gardens, and no definitive archaeological evidence has been found in Babylon.
According to one legend, Nebuchadnezzar II built the Hanging Gardens for his Median wife, Queen Amytis, because she missed the green hills and valleys of her homeland. He also built a grand palace that came to be known as "The Marvel of the Mankind".

Because of the lack of evidence it has been suggested that the Hanging Gardens are purely mythical, and the descriptions found in ancient Greek and Roman writers including Strabo, Diodorus Siculus and Quintus Curtius Rufus represent a romantic ideal of an eastern garden. If it did indeed exist, it was destroyed sometime after the first century AD.

Alternatively, the original garden may have been a well-documented one that the Assyrian king Sennacherib (704–681 BC) built in his capital city of Nineveh on the River Tigris, near the modern city of Mosul.