I was quite surprised to learn that Christie had made a DVD of Sant'Alessio. The opera's cast (commented on by my fellow reviewers), composed entirely of male sopranos and altos, is indicative of the meteoric rise of the castrato in 17th century opera. Compare with Landi's earlier opera, 'La morte d'Orfeo', composed (I think) only nine years earlier, which contains only a couple of castrato roles, an even then only as female parts (due to prohibitions on women appearing on stage). A similar trend can be seen in Monteverdi's operas - 'Orfeo', composed in 1607, only contains three minor castrato parts. By contrast, 'L'Incoronazione di Poppea' (1660's) features several prominent castrato roles.