the greek engineer ctesibius of alexandria is credited with inventing the organ in the 3rd century bc. he devised an instrument called the hydraulis, which delivered a wind supply maintained through water pressure to a set of pipes. the hydraulis was played in the arenas of the roman empire. the pumps and water regulators of the hydraulis were replaced by an inflated leather bag in the 2nd century ad, and true bellows began to appear in the eastern roman empire in the 6th or 7th century ad. some 400 pieces of a hydraulis from the year 228 ad have been revealed during the 1931 archaeological excavations in