The Neoclassical architectural style incorporates the Federal and Greek Revival architectural styles, which were key influences in the late 18th and early 19th centuries. Many of the basic structures of the United States government were built during this time period. The style was popular among European architects because of its simplicity and symmetry. These designs were often used as textbook examples for students to understand the relationship between structure and function. Neoclassicism affected how government buildings are designed today because these designs were ideal for displaying power and authority. The style is also important in history because it was the first major change to government building design since the early days of the Republic. Before Neoclassicism, most government buildings were mostly plain brick or stone structures with some minor decorative details. After Neoclassicism, many new government buildings were constructed in a more elaborate fashion with larger rooms and higher ceilings for administrative use. The Greek Revival style was popular from about 1790 to 1830. It is seen especially in Southern states like Georgia, South Carolina, and Virginia. In these states, many large houses were built during this time using versions of the Greek Revival style. In New York City, where many wealthy Americans lived after the War of 1812, many townhouses were built following the Greek Revival model. These buildings had large rooms on the upper floors with small windows below them for appearance's sake.