The highlight of the S. Broad Street skyscrapers is this most elegant of Burnham's mature Chicago designs. The base was reworked by Burnham and Horace Trumbauer when they added the south tower in 1902, but the vertical leap of the upper levels takes Louis Sullivan's idea of the tall building as a “proud and soaring thing” to its logical conclusions as masonry-clad piers rise to the crowning arches that support the top story. Alternating flat and faceted bays between the piers increase the verticality of this purest Chicago School skyscraper in the east. Interiors have generally been adapted to modern detail, but the interior iron stairs recall the industrial energy of the age.