Second Empire architecture is a French subset of classical revival architecture known for its highly eclectic usage of the orders and different classically-influenced styles. Similar to the later Beaux-Arts style, it employs then-modern materials such as iron and glass to construct larger buildings. Second Empire is among the most richly decorated classical revival styles, the most prominent examples literally having no surface unfinished.
The term "Second Empire" comes from the style's development during the Second French Empire. In the United States, it was called the "French" or "Modern French" style by contemporary architects, but historians have retroactively applied the label Second Empire.
Second Empire architecture became popular in France in the 1850s. An early example is the former Bibliotheque Nationale designed by Henri Labrouste, which combines classical forms with modern iron framing. The style borrowed freely from many predecessors, such as Baroque, Renaissance, and Gothic--it was derided as the "opulent bastard child of all the styles". Paris was renovated by Georges-Eugene Haussmann between 1853 and 1870, and Second Empire architecture was employed on public and private buildings alike.
In the United States, architects admired the French designs of the period, and Second Empire architecture began to be built at the same time. The first major project was the Renwick Gallery, which was completed in 1860. The Civil War created a hiatus in new construction, but after it ended the Second Empire became a popular choice for government buildings by figures such as Alfred Mullett. Residential examples were fewer due to the style's opulence, meaning only the wealthiest businessmen could build houses in it at first. More austere Second Empire houses tended to be Italianate in expression and layout with a mansard roof.
Aesthetically, Second Empire architecture is characterized by its eclectic usage of classical forms and grand scale. Buildings commonly employ multiple orders and have opulent features such as domes, towers, and pedimented entrances. A key feature that often distinguishes Second Empire buildings from other similar styles is its usage of the mansard roof, a steeply pitched design that enables the usage of the attic as an extra story without continuing the facade upward. They commonly have flat facades without porches or loggias, emphasizing their sense of sturdiness and scale. In plan, they are simple and rectangular or square, governed by axes.
The Second French Empire fell in 1870, which marked the demise of the style in both France and the United States. Alfred Mullett resigned from his position as supervising architect for the Treasury in 1874 due to corruption and perception of his designs as frivolously expensive, another stain on the Second Empire style's reputation at the time. The style was employed until the end of the 19th century, though it was surpassed in popularity by others such as Queen Anne and Beaux-Arts.