Square piano by Anton Walter & Son, Vienna, c1800 

Diminutive keyboard instruments, often sounding at octave pitch (called in Italian ottavini) and occasionally concealed in larger pieces of furniture or highly decorated caskets, were built during the 16th and 17th centuries. Sometimes these accompanied larger keyboard instruments operating at the normal pitch of the place in which they were made. Used for private accompaniment and amusement, and occasionally taking the form of other articles, such as household work-boxes, these instruments were both functional and novel. This square piano was, however, probably conceived with portability in mind and sounds at normal pitch. It might have been used for private practice, composition, or for performance in small or outdoor environments. In spite of its size and single stringing throughout the compass of four and a half octaves, it can be heard at a considerable distance. The piano’s action is a miniaturised version of the Viennese action. Gabriel Anton Walter is famous for having built one of the pianos owned by Wolfgang Amadeus Mozart and was renowned in his lifetime. Walter’s stepson, Joseph Schöffstoss, joined him in business in 1800 and this instrument may be among the earliest to survive bearing the names of both makers.