Haydn wrote ca. 160 works for the baryton, a peculiar type of gamba/cello with particular mechanics for the strings. Most of the works were written in the period 1762–1775 and were mainly intended for Prince Nikolaus Esterhazy I, a skillful and avid player of the baryton. The works are extremely beautiful and some even rather demanding: the Esterhazy Ensemble did a wonderful job, presenting this World's first complete recording.
(About the baryton, - video infra - see it played live by Rainer Zipperling)