Refers to the architectural and decorative arts style in France between 1852 and 1870 during first the presidency and later the Empire of Napoleon III, but also affecting Europe and the United States. Noted for its eclecticism, opulence, and ostentation, the period reflects the revival of several historical styles including the Louis XVI, Gothic, Renaissance, and Baroque styles. In architecture, the style is identified more specifically with public and domestic buildings with mansard roofs, heraldic motifs, pedimented dormers, and French Renaissance detailing.

Source: Art & Architecture Thesaurus 

http://vocab.getty.edu/page/aat/300021279