The hydraulis was the earliest precursor to the pipe organ, invented by Ctesibius of Alexandria in the 3rd century BC. It was a remarkable feat of ancient engineering that used water to regulate air pressure. Air was pumped into a metal container submerged in a tank of water; the weight of the water provided constant pressure to push that air through the pipes when a key was pressed. This ensured a steady, even tone, which was previously impossible with manually operated bellows. The hydraulis was widely used in ancient Rome during circuses and theater performances. Because of its power and complexity, it was considered a status symbol. It eventually evolved into the bellows-driven pneumatic organ as water-based systems were prone to corrosion and were much heavier to transport.