Millennia after its destruction, the city of Babylon remains a symbol of extravagance and wealth. Its most celebrated feature was one of the 'Seven Wonders of the World'. The so-called 'Hanging Gardens of Babylon' astounded and perplexed observers. In the first century BC, Diodorus Siculus described them as 'gardens suspended in the air'. From a distance they were described as looking like a terraced hillside, or the rows of seats in a Greek theatre.They are said to have been built for a favoured wife of Nebuchadnezzar who came from the mountainous country in the North. Some experts even believe that the ancient chroniclers got the location wrong and that the gardens were not at Babylon at all, rather that they were built centuries earlier by King Sennacherib of Nineveh. But wherever they were located the mystery remains - how could such elaborate gardens possibly have been irrigated? Ancient sources describe a mysterious, hidden system of irrigation which carried water to the summit. So what was this system and how did it work? Without any archaeological evidence for the gardens surviving this question becomes even more difficult to answer. The experts are divided. John Oleson, an expert on ancient water-lifting devices, believes that a whole series of shadufs may have been used. Commonly used to this day in the Near East, shadufs are basic levers with buckets at one end and a counterweight at the other. But Stephanie Dalley thinks not. Reading his ancient writings, she believes Sennacherib employed screws mounted within tubes to lift water. If this is true, then Sennacherib's engineers invented the Archimedes Screw centuries before Archimedes was born. Water engineer Jo Parker attempts to test both theories by reconstructing each method to see if they were feasible using the technology of the time. However, there is one final challenge to face. Stephanie Dalley insists that the sources say that Sennacherib made his screw out of bronze. Experimental bronze caster Andrew Lacey attempts to cast a bronze screw using only the technology of ancient Mesopotamia. It is the largest object he has ever cast in the field and a highly dangerous process. But will it work?