But for all that the 1609 score must in some sense represent an idealized version of Orfeo, whether as a record of the première or for future performance, its contents are clearly linked to events in 1607 and, in particular, to the performers available to Monteverdi in Mantua at that time. For example, and as one might expect, the rich instrumentation of the opera matches closely the instrumental resources (both instruments and players) available at the Gonzaga court during this period. The same presumably applies to the singers. We already know two of them, the great virtuoso tenor Francesco Rasi as Orfeo, and a castrato imported from Florence, Giovanni Gualberto Magli, who sang La Musica (in the prologue) and probably took at least one other role (although precisely which remains unclear). Close examination of the vocal ranges and style of writing for the various voice-parts needed for Orfeo, however, reveals that Monteverdi was at least initially writing for a precise ensemble, and one that he had used specifically in earlier large-scale theatrical or semi-theatrical works for Mantua such as the madrigal ‘Questi vaghi concenti’ (published in his Fifth Book of madrigals of 1605). ‘Questi vaghi concenti’ is scored for an unusual group of nine male singers (three castratos, two altos, two tenors and two basses) plus string instruments, and it is clear that these same or similar nine singers, plus Rasi as Orfeo, formed the ensemble that Monteverdi and Striggio had in mind at least when designing their opera. But inconsistencies and apparent alterations in the 1609 score (including the revised finale) also reveal that their ideal was compromised by external circumstances, some of which explain the last-minute recruitment of Magli from Florence.
The upshot is that: (a) Orfeo was written for, and at least initially performed by, an all-male cast (itself an interesting issue); (b) Orfeo can be, and probably was, performed by precisely ten singers, nine of whom double up solo roles and variously sing the choruses; (c) the allocation of solo and chorus roles to these singers was carefully planned with a view to the practicalities of staging (e.g., permitting time for costume changes); and (d) hitherto unnoticed but significant alterations in Act IV suggest when the revised Apollo finale was brought into play. The conclusion—radical in terms of the scholarly literature if obvious once one considers it—is that for all Orfeo’s canonic status, it is a work of and for a theatre of a precise time and a precise place, all of whose participants had a profound effect on the shaping of the whole.