Babylon (present-day Iraq) was the city-state of ancient Mesopotamia. Under King Nebuchadnezzar II, the city was a wonder to its visitor for its size & architecture. Herodotus, a historian in 450 BC described Babylon as follows: massive walls of huge size & strength; within the walls, there were fortresses & temples containing statues of solid gold. The famous Tower of Babel, built for the god Marduk, rose high above the city, seemingly piercing into heaven itself. The Hanging Gardens of Babylon was no less spectacular, built around 600BCE.
Yet this Gardens was not mentioned by Herodotus.
King Nebuchadnezzar built the gardens to please his Persian wife Amyitis, whom he married to create an alliance between their nations. She missed her land with its lush greenness & mountains; the dry, sun-baked terrain of her new home was depressing. King Nebuchadnezzar decided to built an artificial mountain with rooftop gardens. The Gardens were destroyed after a series of powerful earthquakes that affected the region after 2nd century BCE.
The Gardens weren't "hanging" as in by ropes/wires; the word "hang" came from an inaccurate translation of the Greek word kremastos/Latin word pensilis which meant "overhanging" as in the case of a balcony/terrace. The Greek geographer Strabo wrote:
"It consists of vaulted terraces raised one above another, & resting upon cube-shaped pillars. These are hollow & filled with earth to allow trees of the largest size to be planted. The pillars, the vaults & terraces were constructed of baked brick & asphalt.
The ascent to the highest story is by stairs, & at their sides are water engines, by means of which persons, appointed expressly for the purpose, are continually employed in raising water from the Euphrates (river) into the garden."
Hence from the account above, we see that the most amazing part of the Garden isn't really the Garden itself but the mechanism that supplies water from the Euphrates River to the Garden on elevated plains. This was probably achieved via a chain pump.
Another issue is to prevent the disintegration of the Garden's foundation from the water. The material used is brick which is clay baked in the sun. Clay bricks dissolve quickly in contact with water (true), so to overcome this problem, the foundation was covered with layers of reeds, tiles, & asphalt.
So there was engineering even back then hehe :p
There are many controversies surrounding the location of the Gardens. Some said it wasn't built by King Nebuchadnezzar II; instead it was built by Sennachrib who ruled Assyria in 705-681BCE. It is possible that over the centuries, the 2 sites were confused & the Gardens were attributed to Babylon instead.
Whatever the truth is, it'll be sought out by archeologists. In the meantime, it is something to muse over whether Queen Amyidia was pleased with the Gardens or still pined for her homeland.