The Duluth Works was an industrial steel and cement manufacturing complex that operated from 1915 to 1987. Owned by U.S. Steel, it was “built as part of a ‘gentleman's agreement’ between U.S. Steel and the State of Minnesota to not impose hefty iron ore taxes on U.S. Steel in exchange for a fully integrated steel plant within Minnesota, whose mines furnished 80% of the ore to U.S. Steel. The combined works of the steel and cement plant were the largest employers in Duluth and the fourth largest industrial complex in Minnesota.” More on Wikipedia.