The Greek geographer Strabo, who described the gardens in first century BC, wrote, "It consists of vaulted terraces raised one above another, and resting upon cube-shaped pillars. These are hollow and filled with earth to allow trees of the largest size to be planted. The pillars, the vaults, and terraces are constructed of baked brick and asphalt."

  We'll start with the most popular theories about the gardens. They were likely located by the Euphrates River in what is now modern-day Iraq. The gardens didn't actually hang: They draped over the sides of terraces on a brick structure. Some accounts of the gardens claim that they grew as high as 75 feet (22.86 meters) in the air and that people could walk beneath them. Accounts from the classical writer Diodorus Siculus describe that the brick walls were 22 feet (6.7 meters) thick and 400 feet (121 meters) wide. And Philo wrote that there were several strata of flora and many levels of irrigation..

  According to legend, King Nebuchadnezzar built the gardens for his wife, Amytis. Amytis was a princess from Media, a region of Iran near the Caspian Sea. Nebuchadnezzar is said to have built the gardens for her as a reminder of her homeland. But it's strange that Nebuchadnezzar, who recorded his many accomplishments in cuneiform, a type of ancient writing used in record-keeping, didn't mention the gardens.This has led some scholars to theorize that the gardens were actually built by an Assyrian queen or even by Sennacherib, the ruler of Nineveh.

    If they existed, the Hanging Gardens of Babylon would be the second oldest of the ancient wonders. Built in the 6th century, the gardens are long gone. Some scholars argue that the reason there's no record of them is precisely because they were gardens -- plants and flowers are living things that eventually die. Even if the structure on which the gardens were affixed remains, it could very well be in unrecognizable ruins.

   Today, our knowledge of the Hanging Gardens of Babylon comes from interpretations of ancient accounts and artists' renderings of the wonder.