The gamba (as it is often foreshortened) comes in 4 sizes: treble, tenor, bass, and double bass. The treble is about the size of a violin; the bass is a bit smaller than a cello.
Much music was composed for the gamba in the 16th and 17th centuries. The bass viola da gamba continued to be used (as a solo instrument) into the 18th century; composers such as Johann Sebastian Bach and Karl Friedrich Abel wrote music for it.