Abstract
This essay investigates the visual language of Guercino's monumental altarpiece of St Petronilla for St Peter's (1623), through which he constructs an authoritative image of her sanctity deeply intertwined with the art and fabric of the renewed church, particularly as it pertains to Michelangelo's legacy at the site. The saint's body, almost in tandem with the sculptor's Pieta, circulated throughout the old and new basilica during its gradual demolition and reconstruction. Guercino's imagery consolidates references to Petronilla's relics, her cult and the statue in the configuration of the saint suspended at her grave. A hitherto unnoticed portrait of Michelangelo underscores these associations and renews his exemplarity as a sacred artist in the service of the papacy. The evocations of Michelangelo's sculpture and person, the body of Petronilla, together with the altarpiece's setting and architectural imagery, encourage an interpretation of the altarpiece as a microhistory of St Peter's basilica itself.