How the Seven Wonders of the Ancient World Work

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.

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.

The gardens wouldn't have been the only grand sight in Babylon. This ancient city was filled with shining palaces and sturdy ziggurats. Even the city gates were adorned with carvings and gleamed with glazed bricks [source: Smithsonian]. But in a desert country as dry as Iraq, canopying fronds and blooms would have been an awesome sight to see.

If Babylon's buildings boasted of its great wealth, then the gardens would've demonstrated the engineering skills of their architect. It's no small feat to keep plants thriving in the desert, but to transport water to flowers perched atop a nearly five-story building is a monstrous challenge. The gardens would have relied on the Euphrates as their irrigation source, and the water would likely have been transported through a pumping system made of reeds and stone and stored in a massive holding tank. From the tank, a shaduf (a manually-operated water-lifting device) would have delivered water to the plants.

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.

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

In the next section, we'll travel to Turkey to explore the Temple of Artemis at Ephesus.