was completed on this date in 1884 when workers placed the 3,300 pound marble capstone on the Washington Monument and topped it with a nine-inch pyramid of cast aluminum. Construction on the privately funded 555-foot monument had begun in 1848, but was suspended (at 156 feet) for 20 years due to lack of funds. The U.S. Army Corps of Engineers finished the project. When completed it was the world’s tallest structure; today it is the world’s tallest freestanding masonry structure.