The article reconstructs the pictorial and sculptural decorations of the Florenzi chapel in San Silvestro al Quirinale in light of the unpublished contract underwritten by Cesare Nebbia in 1579. In addition to unequivocally identifying the patron as the Umbrian prelate Marc'Antonio Florenzi and establishing a precise chronology, the document reveals the involvement of Girolamo Muziano as financier and guarantor of the project in particular ways different from common practice for artistic agreements of the time. The contractual stipulations underscore the dynamics of exchange and dialogue between Muziano and his protégé Nebbia, both in terms of graphics and of the relationship with his patron at the worksite where they collaborated in ways hitherto unrecognized in the literature.