We are used to thinking of ‘opera singer’ as a profession. But no such profession existed when opera emerged as a genre at the turn of the sixteenth and seventeenth centuries, when the first public opera house opened in Venice in 1637, or for three or four decades after that: operas were too few to occupy most of anyone's time. In the early seventeenth century not even ‘singer’ was as yet a clearly defined trade. Many singers were also instrumentalists: some accompanied themselves (and some also composed their own music), while others switched between singing and playing; the commonest Italian term for them all was musici. Others again were actors or actresses who could sing, like Virginia Andreini, drafted in an emergency to create the title part in Monteverdi's Arianna of 1608.