Octagon house
Octagon houses were a unique house style briefly popular in the 1850s in the United States and Canada. They are characterised by an octagonal (eight-sided) plan, and often feature a flat roof and a veranda all round. Their unusual shape and appearance, quite different from the ornate pitched-roof houses typical of the period, can generally be traced to the influence of one man, amateur architect and lifestyle pundit Orson Squire Fowler. Although there are other octagonal houses worldwide, the term octagon house usually refers specifically to octagonal houses built in North America during this period, and up to the early 1900s.
History
Early examples, before Fowler:
Poplar Forest, Thomas Jefferson's private retreat and plantation house near Lynchburg, Virginia.
William Thornton's Tayloe House, more commonly called The Octagon House in Washington, DC. After the White House was burned by the British during the War of 1812, President James Madison stayed in the Octagon House, and it was here that the Treaty of Ghent (ending the War of 1812) was signed. It is now the headquarters of the American Institute of Architects. While known as "The Octagon", it is worth noting that this particular building is not actually octagonal.