Here are some views of the Piazza San Pietro (St. Peter's Square) in Rome.  The first is an anonymous image of the piazza prior to its renovations which began in the 1650s under Pope Alexander VII.  Notice the complete lack of the colonnaded porticoes that the space is now known for.  The second is an image of Bernini's planned porticoes by Giovanni Battista Falda from about 1665.  Significantly, the image shows the “terzo braccio” on the eastern side of the square which was, in fact, never built.