Laying the Foundation for the Old Saint Peter's Basilica

The scene depicts the transition of power and the building of a new spiritual order, with Emperor Constantine kneeling to remove the first basket of earth. To the right, an assistant holds up a parchment displaying the architectural floor plan of the basilica, while laborers with shovels begin the excavation. The work is painted in a monochromatic brown wash, designed to mimic the appearance of a classical marble bas-relief.

This fresco illustrates the 'Donation of Constantine' narrative, a cornerstone of Vatican political philosophy asserting the Church's inherited authority from the Roman Empire. The depiction of the architectural plan reflects the Renaissance obsession with the 'Vitruvian' ideal of sacred architecture and the restoration of ancient Roman grandeur within a Christian framework.