Archimedes' screw, also called the Archimedean screw or screwpump, is a machine historically used for transferring water from a low-lying body of water into irrigation ditches. Water is pumped by turning a screw-shaped surface inside a hollow pipe. The screw pump is commonly attributed to Archimedes on the occasion of his visit to Egypt. This tradition may reflect only that the apparatus was unknown to the Greeks before Hellenistic times and was introduced in Archimedes' lifetime by unknown Greek engineers. Some writers have suggested the device may have been in use in Assyria some 350 years earlier. Etching from 1769.