December 6

On December 6, 1884, the Washington Monument was completed with the placement of a nine-inch aluminum pyramid at its top, 555 feet in the air. The original design by architect Robert Mills included a Greek temple at the base. Construction began on July 4, 1848, though funds fell far short of the $1 million needed. Work halted in 1854-1877 due to obstruction by the nativist Know-Nothings, lack of funds and the Civil War. Construction resumed with visibly different exterior marble. The monument is the world's tallest stone structure and tallest true obelisk. The apex was the largest single piece of aluminum cast at the time, when the metal cost nearly as much as silver. The apex was put on public display beforehand and stepped over by visitors who could say they had "stepped over the top of the Washington Monument." Pictured: Instagram, National Park Service.