The Hanging Gardens of Babylon, which are generally thought to have been built in the sixth century BC, are known as one of the Seven Wonders of the Ancient World. They were said to have been constructed by Nebuchadnezzar II to appease his wife Amytis, who complained about the lack of lush vegetation in Babylon compared to her homeland. Although many visitors from Greece wrote about the Hanging Gardens of Babylon, there is no recorded mention of them by Nebuchadnezzar II himself, leading modern scholars to believe that they may never have existed at all.
Other modern academics, such as the Assyriologist Stephanie Dalley, have put forward evidence that suggests the Hanging Gardens of Babylon were located far outside of the city of Babylon. Based on a careful study of ancient texts, Dalley proposed their real location to be Niveneh, which is located not on the Euphrates River like Babylon, but on the Tigris, 340 miles north of Babylon's location in modern-day Iraq.
Whether or wherever they existed, the Hanging Gardens of Babylon were not said to have been suspended in the air as their name suggests. Rather, they were gardens planted on roof tops, which had been waterproofed with reeds and tar.