 Historically the industry had been dominated by individuals and small firms who combined the roles of architect and engineer, but this broke down in Chicago during the period, being replaced by a partnership between specialist architects who focused on the appearance of the skyscraper, and specialist engineers who focused on the structures that enabled it to be built.Chicago architectural firms grew to be large, hierarchical and with numerous specialist staff; the D. H. Burnham & Company, for example, felt like a small factory to visitors, and ultimately expanded to employ 180 staff.The resulting Chicago school produced large, solid-looking skyscrapers, built with a common appearance and to a common height.