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 said to be a distinctive feature of ancient Babylon and a great source of pride to the people. The gardens are believed to be a 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 bud bricks.
This hand-coloured engraving, probably made in the 19th century after the first excavations in the Assyrian capital. depicts the fabled Hanging Gardens, with the Tower of Babel in the background:
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 11, who ruled between 605 and 562 BC. There aare no extant Babylonioan texts which mention the gardens, are no definitive archaeological evidence has been found n Babylon.
According to one legend, Nebuchadnezzar 11 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 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 as destroyed sometime after the first century AD.
This a 20th century interpretation of the Hanging Gardens:
There is a lot more on Wikipedia about the Hanging Gardens. If you are interested you might take a peek and then decide if the gardens did actually exist.