The aulos is a class of reed instrument and, specifically, the most important wind instrument of the ancient Greeks. The term is derived from the Greek word for blowing. Although the aulos differed in size and shape, it was usually a double-pipe instrument, with one pipe longer than the other. The treble and bass pipes were played simultaneously by one performer. It had a double reed. The aulos came in several sizes and was often played in pairs. It was inserted in the mouth so the performer could use his mouth cavity as a wind bag and blow continually while inhaling air through his nose.