Traditionally, frescoes of the Last Judgement have always had their place on the west wall, the wall of the entrance into the space of the church. Were we to assume that this large-format drawing is a sketch for such a painting, then the round opening could be readily explained as a rose window. This interpretation is contradicted by the drawing in sanguine, which was added at a later time; such drawing can be found on sketches for stained glass windows, where it indicates the boundaries of the individual fields of glass. More recent researchers have therefore concluded that our sheet is to be considered a sketch for a stained glass window, although this theory is unable to account for the empty circular form.