In evidence that they discovered were deep trenches

In the ancient world
there were 7 wonders of the world and the Hanging Gardens of Babylon was one of
them.  The Hanging Gardens were described
as beautiful gardens with many trees, plants, and shrubs. They were supposed to
represent a green mountain. They were depicted as a ziggurat looking structure.
A ziggurat was a multiple floored building that was popular in the Babylonian

Hanging Gardens were believed to be constructed by King Nebuchadnezzar, who was
king of the Babylonian empire from around 605 to 562 B.C.  Being one of the 7 ancient wonders, the Hanging
Gardens have been studied by many historians and archaeologists, but there has
been little to no evidence of their existence. 
The little evidence that they discovered were deep trenches and walls
that could have been used for water and soil storage so that the plants had
what they needed to flourish. 

are two speculations on the gardens.  The
first one is that they were just a myth and the writers who wrote about them
were basing them off of another garden. 
The other speculation is that they were built in a southern province
called Nineveh by a King whose name was Sennacherib.  The reason they were constructed was for the
purpose of reminding the king’s wife, Queen Amytis, of her homeland. 

gardens were described as a tall palace held up by columns with plants
everywhere.  The building itself was said
to be in many tiers.  It was 50 cubits,
or 75 feet tall, and it was 400 feet wide and 400 feet long and the walls were
made of 22 inch thick bricks.  It also
had many columns which were hollow, which allowed them to fill them with soil
so the roots of the plants could grow. 
That way the plants could be kept alive. 
They had a system where they had a chain of buckets near the Euphrates
River and the buckets would be pulled up to the top to water the plants.  These platforms were made of stone with reeds
and covered with asphalt and tiles with lead as the base, so the platforms did
not rot when they watered the gardens.

the Hanging Gardens did exist, they were said to have been destroyed by an
earthquake around the 2nd century B.C. and the remains, overtime,
possible slowly eroded with the rain.