What musical instrument did Leonardo da Vinci design as a keyboard-operated viola?

Leonardo da Vinci designed the viola organista as a keyboard-operated bowed string instrument.

The concept combines features of a keyboard and a string instrument. Pressing keys would select notes, while rotating wheels or belts would rub against strings and produce a sustained sound. Unlike a conventional piano, in which hammers strike strings, the viola organista was intended to imitate the continuous tone of bowed instruments.

Leonardo drew several versions of the idea in his notebooks. The exact construction changed from one design to another, and the surviving sketches do not provide one completely standardized instrument. This is why modern builders have produced different reconstructions.

The viola organista was not a normal viola and was not part of the modern orchestral instrument family. It was an experimental keyboard instrument that shows Leonardo combining acoustics, mechanics, and musical performance in a single design.