Notman made even greater changes in the exterior appearance. Two of the three entrances at the front of the building were removed and towers built on either end to house the stairways that were removed from interior halls. The doorway at the center of the building was replaced by a larger, arched doorway of Florentine style with more massive steps below and a similarly arched window, with a balcony, above. The vertical emphasis thus achieved culminated in a cupola even loftier than Latrobe's.

Source: Leitch p. 328ff