A string quintet is an ensemble of five string instrument players or a piece written for such a combination. The most common combinations in classical music are two violins, two violas and cello or two violins, viola and two cellos. The second cello is occasionally replaced by a double bass, as in Antonin Dvorak's quintet. Wolfgang Amadeus Mozart pioneered writing for a string quartet augmented by a second viola, and one outstanding masterpiece for the two-cellos quintet is Franz Schubert's Quintet in C major.