From the Chicago Architecture Foundation:
Praised in 1888 as the largest and finest office building in the country--all eleven stories-- The Rookery featured both masonry load-bearing walls and skeletal fram construction. Architect John Wellborn Root lavished exquisite care on The Rookery, built on the site of the former City Hall and named after its dity pigeons and corrupt politicans. Frank Lloyd Wright modernized The Rookery in 1905, changing the light fixtures and covering old dark iron surfaces with incised Carrara marble. Today The Rookery stands as a first-class office building. Hardcover, 64 pages, 55 contemporary and historic images.