“L’inganno degli occhi”. Borromini’s perspectival niche for the Casa dei Filippini in Rome

The RCIN 905602 sheet of the Royal Collection, Windsor contains an orthogonal projection presentation drawing made by Francesco Borromini in 1627 and showing one of Gianlorenzo Bernini's proposals for the Tomb of Urban VIII. The apsidal frame rendered in perspective can be related to the perspective niche that Borromini himself placed above the fictitious entrance in the center of the facade of the Casa dei Filippini in Rome a few years later. The sheet is studied here in the context of the influence that the diffusion of representation methods and practices has had on the forms of architecture as well as their visual perception. After discussing the reason for the construction of such a perspective device, its representation in the design documents and its reception in the images of the square after its construction, the authors present the results of a geometric analysis and reconstruction after photo-modeling ot the niche itself, aimed at determining the position of the ideal observer on the square considered in designing the device, and they discuss the relationship between this spatial stratagem and the graphic trick atopted in the tomb design.