The Three Gorges Dam contains enough steel to build 63 Eiffel Towers.

The Three Gorges Dam is a 'gravity dam' which means it uses its own incredible weight to hold back the Yangtze River. To make it strong enough, engineers used 463,000 tonnes of steel bars hidden inside 27.2 million cubic meters of concrete.Concrete is great at being squeezed, but it can snap if it is pulled or bent. The water in the reservoir weighs about 40 billion tonnes and pushes against the dam with massive force. The steel skeleton inside acts like a giant cage that keeps the concrete from cracking under all that pressure.Building this giant was a huge challenge that started in 1994. When concrete dries, it gets very hot, sometimes reaching over 70°C (158°F). If it cools too fast, it cracks, so engineers ran cold water through pipes inside the walls to keep it cool.The finished dam is 2,335 meters (7,660 feet) long and 181 meters (594 feet) high. It holds back so much water that it could fill 16 million Olympic-sized swimming pools. Without that massive steel skeleton, the dam would never be able to stand up to the power of the river.