What is the Eiffel Tower made of?

To erect a tower 1,000 feet (300 m) high, Gustave Eiffel and his engineers had only one material at their disposal: iron. Wood was hardly a realistic option. A stone tower would have collapsed under its own weight. And reinforced concrete was still in its infancy. But iron was a material that had been perfectly mastered both in its production and in its implementation. It had been known since the 2nd century BC, but it wasn’t until the 1850s that its use became widespread in construction thanks to its industrial availability. 

The cast iron produced in blast furnaces by reducing iron ore is then refined by an operation called puddling, which removes the excess carbon still present in the cast iron. The result is almost pure iron. It can then be rolled into plates or simple profiles of L or I sections that can be easily assembled with rivets to form light and strong structures. 

Why iron and not steel?

The iron of the Tower comes from the Forges de Pompey near Nancy. Why did Eiffel prefer iron to steel, a similar material but more resistant thanks to a more controlled manufacturing process and one which was beginning to be used in construction? Simply because he had more confidence in iron, which he had used in all his previous constructions.