An early type of pipe organ, the hydraulis, was invented in the third century BC by Greek engineer Ctesibius and used water as its main source of energy. It hasn’t drastically changed throughout history—its complex and sophisticated mechanism of pipes, pressure regulators, piston pumps, and valves is a great piece of engineering. It’s also the loudest instrument in the entire mechanical armory, filling vast spaces with magnificent, awesome sounds. French composers, inspired by the instruments built by master organ craftsman Aristide Cavaillé-Coll, expanded its repertoire substantially and superbly.