Washington Monument

A marble obelisk honouring George Washington; a colour change a third of the way up marks a 23-year pause in construction.

Building started in 1848, but money ran out and the work stopped for more than 20 years. When the stone tower was finally finished in 1884, it was the tallest structure on Earth, a title it held until the Eiffel Tower opened in Paris in 1889. Today it is one of the best-known sights in the city, standing between the U.S. Capitol and the Lincoln Memorial, ringed by 50 American flags, one for each state.

Why it has two colours

Look closely and you will see that the stone changes colour about a third of the way up. Construction began in 1848 with money raised from the public, but by 1854 the society in charge had run out of funds. Arguments over who controlled the project and then the American Civil War kept it half-finished, a stubby tower, until 1877. When work restarted, the builders could no longer get stone from the original quarry, so the upper part was built with marble from a different place. That is why the lower and upper sections do not quite match.

How it was built

The architect Robert Mills first imagined a grand temple with columns around the base and a statue of Washington driving a chariot, but there was never enough money. Instead, engineers built a plain obelisk, using the ancient Egyptian proportion of making the height about ten times the width of the base. The walls are thick at the bottom and grow thinner as they rise. In December 1884 workers set a capstone weighing about 1,500 kilograms on top, crowned with a small pyramid of aluminium, a rare and costly metal at the time.

Inside the monument

The tower is hollow. An iron staircase of 897 steps spirals up the inside walls, and a lift runs up the middle to an observation level with eight small windows at the top. Set into the inside walls are 193 carved memorial stones given by states, cities, groups and even other countries. Visitors now ride the lift; since 1976 the stairs have been closed except by special arrangement. The monument was shut for repairs after an earthquake in 2011 and reopened in 2014.

On the globe

The model shows the tall white marble obelisk in Washington, D.C. Zoom in and look for the slight colour change a third of the way up, the mark left by the 23-year pause in building.