THE FRONT, or principal elevation, of a building may represent the character of its interior; alternatively it may express its character or its function, for example the urban cinema of the 1930s as a place of dreams and fantasy. Or it may do neither, whether because nobody thought that it mattered or – a fourth alternative – because the architect set out, for aesthetic reasons, deliberately to mislead. Of the two façades compared in the epigraph and illustrated in fig. 1, that on the right, of the Chiesa Nuova (S. Maria in Vallicella), Rome, has more to do with expression than with representation, because it is considerably larger than the cross-section of the building behind it. That on the left is, in its architect's own description, an expression as well as, in another phrase, a device ‘to deceive the eye of the passer-by’.