In lanscape architecture and garden design, a water feature is any of a full range of fountains, pools, ponds, cascades, waterfalls, and streams. Prior to the eighteenth century they were usually powered by gravity, though the famous Hanging Gardens of Babylon are believed to have been supplied by an Archimedean screw. Other examples were supplied with water using hydraulic rams. Since the eighteenth century the majority water features have been powered by pumps. The power source was sometimes a steam engine but in modern gardens it is almost always electricity. There is an increasing range of innovative designs as the market becomes more established and people become more aware of the advantages of using solar power. These advantages include environmental benefits, no mains electricity in the garden, and free energy.