Cappella di Isotta (detail)
by AGOSTINO DI DUCCIO, Photo
Above a relief of angels, the picture shows the SI monogram (from the initial of Sigismondo and Isotta’s names, or, according to others, the first two letters of the former).
The reconstruction of the church was commissioned by Sigismondo Pandolfo Malatesta from Leon Battista Alberti around 1450, and his monogram is present in numerous other places in the church.