A lot of people have heard of The Hanging Gardens of Babylon, but few know why these gardens were considered by the Greeks to be one of the Seven Wonders of the World. The irrigation system alone is a mystery worthy of its own Secrets episode. How were such elaborate gardens watered? No one really knows, but attempts to test various theories have been made by modern water engineers using technology of the time and this series follows those attempts. At least these Babylonians didn't have to face the modern-day difficulty of a hose-pipe ban.