Leonardo da Vinci designed the viola organista to make continuous music with a keyboard and rotating bow.
Unlike a conventional keyboard instrument, the viola organista used moving wheels to bow strings. The player pressed keys to select notes, while the wheel mechanism maintained contact with the strings. This arrangement aimed to combine the controllable pitch of a keyboard with the sustained sound of a bowed instrument.
Leonardo developed more than one version of the idea in his notebooks. The surviving drawings show his interest in translating rotational mechanical motion into sound. Because the mechanism was complicated, the instrument remained a design rather than a successful commercial invention during his lifetime.
The viola organista is distinct from a piano, whose hammers strike strings, and from a harpsichord, whose jacks pluck them. It is also not simply an ordinary viola. Its hybrid construction makes it one of Leonardo's clearest examples of invention at the boundary between engineering and music.