The baryton/or viola di bordone or viola bardone/

is a plucked stringed instrument with a characteristic sound. It dates from the latter half of the 17th century and remained popular until the early 19th century. Initially, it was made by adding to the six or seven bowed strings of a specially built tenor-bass viola da gamba another register of metal strings (8-20 or even more). These being sympathetic strings, their resonance provided the instrument with its unique sound. In addition, they could even be plucked behind the neck of the instrument with the left thumb.

Leopold Mozart in his Violinschule (1756), had this to say about the baryton: "Like the gamba, this instrument has six to seven strings. The neck is very broad and the reverse side is hollow and open, with some nine or ten brass or steel strings stretched there, which are touched and plucked with the thumb in a way that allows the principal part to be played with the bow on the upper, gut strings, while the bass is plucked with the thumb on the strings stretched under the neck. This is precisely why the pieces for the baryton have to be composed in a special way. Apart from that, it is one of the most charming instruments."

The first to describe the baryton and the way it is played was Daniel Speer in his tutor Unterricht der Musikalischen Kunst, published in 1687 in Ulm: "There exists yet another viola which surpasses all the others, called viola di bordone. But one finds very few musicians who can play on it."

The oldest baryton known to us is a Viennese instrument made about 1655, and the earliest works were written specifically for the baryton around 1670. At that time there was wide variation in the tuning and number of the strings, both those played with a bow and the sympathetic, plucked ones. This is also borne out by the surviving original compositions and by the approximately thirty baryton gambas of the time to be found in museums, most of which are in too poor condition to be played.

One of the lucky exceptions to this is a baryton Johann Joseph Stadlmann made in 1750 in Vienna for Prince Miklós Esterházy. It has seven strings for bowing and ten sympathetic ones for plucking. Today the instrument is in the Hungarian National Museum, but it is played on special occasions.
Joseph Haydn took service in 1762 as Kapellmeister to Prince Miklós Esterházy, who was passionately fond of the baryton and played it very well himself. Prince Miklós, known as the Magnificent, was constantly encouraging the musicians in his court orchestra to write new works for the instrument. He also encouraged Haydn "to fling himself more diligently than hitherto into composition, and particularly into writing pieces that can be played on the gamba, of which we have still seen very few."

The instrumental ensemble that featured most frequently at the Prince's court was a trio consisting of a baryton, a viola and a cello. Today we know 126 such baryton divertimentos by Joseph Haydn himself, many others are known to have existed, but have disappeared.

At the Prince's court, the baryton was always tuned with bowed strings of D-G-c-e-a-d, and sympathetic, plucked strings of A-d-e-f sharp-g-a-b-c sharp-d. Haydn scored both parts in the treble clef, an octave higher than they sounded. Haydn indicated which plucked strings to use by numbering them l to 9 under the notes. The tuning of these strings also decided the keys in the works. Most of them are in D major, or more rarely in A major and G major. Flat keys scarcely ever occur.