A round barn is a historic barn design that could be octagonal, polygonal, or circular in plan. Though round barns were not as popular as some other barn designs, their unique shape makes them noticeable. The years from 1880–1920 represent the height of round barn construction. Round barn construction in the United States can be divided into two overlapping eras. The first, the octagonal era, spanned from 1850–1900. The second, the true circular era, spanned from 1889–1936.