Detlef Lienau (17 February 1818 – 29 August 1887) was a German architect born in Holstein. He is credited with having introduced the French style to American building construction, notably the mansard roof and all its decorative flourishes. Trained at the École des Beaux-Arts, Paris, he designed virtually every type of Victorian structure—cottages, mansions, townhouses, apartment houses, hotels, tenements, banks, stores, churches, schools, libraries, offices, factories, railroad stations, and a museum. Lienau was recognized by clients and colleagues alike as one of the most creative and technically proficient architects of the period, and was one of the 29 founding members of the American Institute of Architects.