Pittsburgh is the “Steel City”, because at one point, in 1911, Pittsburgh produced more than half of all the steel in the United States. During World War 2, it was one third and the steel mills were running 24h a day. Pollution of the environment was unbelievable and in 1868, James Parton called Pittsburgh being "hell with the lid off”. Here is more information: https://backpackandsnorkel.com/USA/Pittsburgh/#General-Information-about-Pittsburgh