When did the viola join the orcherstra?

Answer 1

The question is odd, since the viola da braccio (the 'arm viol') preceded the Orchestra by centuries.

The term 'viola' has been used for stringed instruments played by a bow, whether held on the shoulder or lap (oriented with the arm, therefore viola da braccio) or held vertically, resting on the calves, or thighs for smaller instruments (therefore viola da gamba), and the earliest iconic evidences of viola-sized instruments, played with a bow and held on the shoulder with f-shaped sound holes and the characteristic scroll, date back to the 1534-5 frescoes of the Sanctuary of Soranno dome.

However, the viola in the strict f-holes and scroll sense, is preceded by close relatives, known as vielles (for which an absolute data is not known.

Certainly, violas (as 'alto violins') were known to Michael Praetorius, who documented them with engravings and string-pitch and range notation in his 1620 Theatrum Musicum, part of his Syntagma Musicum.

In actual fact, the question is beggared by the word "Orchestra". In Italy, the term originally meant a place, not the organization. During the Baroque era, the first group that might have been called an Orchestra in France, the Vingt-Quatre Violons Du Roi, consisted of six Violins and six Bass de Violon (likely to have been Violone or perhaps the 3-stringed bass that persisted into Beethoven's orchestras) and six violas on each of three inner parts (which would have made the ensemble much more sonorous and listenable than 24 violins, alone, might have been!) All of this before the 18th Century even began.

So really, there is no question of the viola joining the orchestra: by the time the term changed from referring to the place where the ensemble sat to the instrumentalists and their instruments, the viola was as entrenched as the violin. Why would this be?

Essentially, the instruments of the Renaissance tended to be made in families. We see this behavior still today, since Adolphe Sax chose to invent his eponymous Saxophones in a family of interleaved sizes pitched in Bb and Eb; likewise, the Clarinets have adopted that sizing and those pitches. Recorders come in Soprano and Tenor, pitched in C, and Sopranino, Alto, and Bass pitched in F. The violin family instruments were created on much the same principal, although with a few exceptions, the job of tenor and alto is taken by the viola alone: The violin is pitched a fifth above the viola, the cello is an octave below the viola, and the adept string player of Praetorius' time was expected to be able to read treble, bass, and the C clefs on any line with equal facility. This means that any violinist or violist could easily trade instruments (or carry both), and with some acclimation, play cello as well... and bass, although the bass's size is immense by comparison to the cello, and it was tuned in fourths (like the viols and violone).

So separating the viola from the violins was conceptually as foreign as the modern concept of an experienced driver being unable to switch from a luxury car to a sub-compact!