Leonardo da Vinci designed the viola organista as a keyboard instrument whose strings were sounded by a continuously moving bow mechanism.
Leonardo drew several versions of the instrument, especially in manuscripts from the late 15th century. Pressing keys selected strings, while a rotating wheel or set of wheels moved a bow against them. This combined the keyboard layout of an organ or harpsichord with the sustained sound of bowed string instruments.
The viola organista was a design rather than a widely produced Renaissance instrument. No surviving original built by Leonardo is known. Modern makers have constructed working versions from his drawings, but these reconstructions differ in details because the sketches leave some mechanisms open to interpretation.
It is often confused with a conventional viola because of its name. Unlike a viola, it was played from a keyboard and did not require the performer to move a bow by hand.