The monochord is a very old instrument. It was used by Pythagoras in ancient Greece to study chords (two or more notes played together). Chords were played by dividing the string into two different lengths with a moveable bridge, then plucking both sides of the string. The chords were described as ratios of string lengths, such as, 2/1 (octave), 3/2 (third), 5/4 (fifth), etc..
The monochord typically had one (mono) string but through the centuries more strings were added. In Medieval and Renaissance times the monochord was used to teach music and play simple songs.
