The documentary series, Une histoire de la musique à travers ses instruments (A History of Music Through its Instruments), takes a look at the history of the instruments used in Western music. Here, you can find out more about the viol.
While its origins remain unclear, it is generally accepted that the viola da gamba came about in the second half of the fifteenth century. Its ancestor was the vielle, the old medieval bow. This instrument's appearance changed a lot throughout the first 100 years of its existence, until it was finally stabilised in the 1600s. The idea that the viola was the ancestor of the violin has proven to be false. These two families of instruments were born less than a century apart and were developed in parallel.