CLAVICYTHERIUM, a name usually applied to an upright spinet (q.v.), the soundboard and strings of which were vertical instead of horizontal, being thus perpendicular to the keyboard; but it would seem that the clavicytherium proper is distinct from the upright spinet in that its strings are placed horizontally. In the early clavicytherium there was, as in the spinet, only one string (of gut) to each key, set in vibration by means of a small quill or leather plectrum mounted on a jack which acted as in the spinet and harpsichord (q.v.). The clavicytherium or keyed cythera or cetra, names which in the 14th and 15th centuries had been applied somewhat indiscriminately to instruments having strings stretched over a soundboard and plucked by fingers or plectrum, was probably of Italian  or possibly of south German origin. Sebastian Virdung,  writing early in the 16th century, describes the clavicytherium as a new invention, having gut strings, and gives an illustration of it. (See Pianoforte.) A certain amount of uncertainty exists as to its exact construction, due to the extreme rarity of unrestored specimens extant, and to the almost total absence of trustworthy practical information.
In a unique specimen with two keyboards dating from the 16th or 17th century, which is in the collection of Baron Alexandre Kraus,  what appear to be vibrating strings stretched over a soundboard perpendicular to the keyboard are in reality the wires forming part of the mechanism of the action. The arrangement of this mechanism is the distinctive feature of the clavicytherium, for the wires, unlike the strings of the upright spinet, increase in length from left to right, so that the upright harp-shaped back has its higher side over the treble of the keyboard instead of over the bass. The vibrating strings of the clavicytherium in the Kraus Museum are stretched horizontally over two kinds of psalteries fixed one over the other. The first, serving for the lower register, is of the well-known trapezoid shape and lies over the keyboards; it has 30 wire strings in pairs of unisons corresponding to the 15 lowest keys. The second psaltery resembles the kanoun of the Arabs, and has 36 strings in courses of 3 unisons corresponding to the next 12 keys, and 88 very thin strings in courses of 4, completing the 49 keys; the compass thus has a range of four octaves from C to C. The quills of the jacks belonging to the two keyboards are of different length and thickness. The jacks, which work as in the spinet, are attached to the perpendicular wires, disposed in two parallel rows, one for each keyboard.
There is a very fine specimen of the so-called clavicytherium (upright spinet) in the Donaldson museum of the Royal College of Music, London, acquired from the Correr collection at Venice in 1885.  The instrument is undated, but A.J. Hipkins  placed it early in the 16th or even at the end of the 15th century. There is German writing on the inside of the back, referring to some agreement at Ulm. The case is of pine-wood, and the natural keys of box-wood. The jacks have the early steel springs, and in 1885 traces were found in the instrument of original brass plectra, all of which point to a very early date.
A learned Italian, Nicolo Vicentino,  living in the 16th century, describes an archicembalo of his own invention, at which the performer had to stand, having four rows of keys designed to obtain a complete mesotonic pure third tuning. This was an attempt to reintroduce the ancient Greek musical system. This instrument was probably an upright harpsichord or clavicembalo.
For the history of the clavicytherium considered as a forerunner of the pianoforte see Pianoforte.
 Mersenne, Harmonie universelle (Paris, 1636), p. 113, calls the clavicytherium "une nouvelle forme d'épinette dont on use en Italie," and states that the action of the jacks and levers is parallel from back to front.
 Musica getutscht und auszgezogen (Basel, 1511).
 See "Une Pièce unique du Musée Kraus de Florence" in Annales de l'alliance scientifique universelle (Paris, 1907).
 See illustration by William Gibb in A.J. Hipkins's Musical Instruments, Historic, Rare and Unique (1888).
 History of the Pianoforte, Novello's Music Primers, No. 52 (1896), p. 75.
 L'Antica Musica ridotta moderna prattica (Rome, 1555).
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)