During the Renaissance in Italy and France, many buildings had steep, double-sloped roofs. An enormous sloping roof crowned the original Louvre Palace in Paris, constructed in 1546. A century later, the French architect François Mansart (1598-1666) used double-sloped roofs so extensively that they were coined mansard, a derivation of Mansart's name.
When Napoleon III ruled France (1852 to 1870), Paris became a city of grand boulevards and monumental buildings. The Louvre was enlarged, sparking a new interest in the tall, majestic mansard roof.
French architects used the term horror vacui - the fear of unadorned surfaces - to describe the highly ornamented Second Empire style. But the imposing, nearly perpendicular roofs were not merely decorative. Installing a mansard roof became a practical way to provide additional living space in the attic level.
Second Empire architecture spread to England during the Paris Exhibitions of 1852 and 1867. Before long, French fever spread to the United States.
Next... Second Empire in the USA.