 Steel-making was a prominent industry in Monessen, which was a Rust Belt borough in the "Mon Valley" of southwestern Pennsylvania that became a third-class city in 1921.Monessen is part of the Pittsburgh metropolitan area, the Rivers of Steel National Heritage Area, as well as the Laurel Highlands.Monessen, named for the Monongahela River and the industrial German city of Essen, was created by land speculators fairly late in the history of the Mon Valley, after neighboring towns had already been settled.