Pittsburgh a center of wartime production. Carnegie worked with others in establishing a steel rolling mill, and steel production and control of industry became the source of his fortune. Carnegie had some investments in the iron industry before the war. After the war, Carnegie left the railroads to devote his energies to the ironworks trade. Carnegie worked to develop several ironworks, eventually forming the Keystone Bridge Works and the Union Ironworks, in Pittsburgh. Although he had left the Pennsylvania Railroad Company, he remained connected to its management, namely Thomas A. Scott and J. Edgar Thomson. He used his connection to the two men to acquire contracts for his Keystone Bridge Company and the rails produced by his ironworks. He also gave the stock to Scott and Thomson in his businesses, and the Pennsylvania was his best customer. When he built his first steel plant, he made a point of naming it after Thomson. As well as having good business sense, Carnegie possessed charm and literary knowledge. He was invited to many important social functions, which Carnegie exploited to his advantage. Carnegie, through Keystone, supplied the steel for and owned shares in the landmark Eads Bridge project across the Mississippi River at St. Louis, Missouri (completed 1874). This project was an important proof-of-concept for steel technology, which marked the opening of a new steel market. Carnegie believed in using his fortune for others and doing more than making money. He wrote: Industrialist 1875–1900: Steel empire Carnegie made his fortune in the steel industry, controlling the most extensive integrated iron and steel operations ever owned by an individual in the United States. One of his two great innovations was in the cheap and efficient mass production of steel by adopting and adapting the Bessemer process, which allowed the high carbon content of pig iron to be burnt away in a controlled and rapid way during steel production. Steel prices dropped as a result, and Bessemer steel was rapidly adopted for rails; however, it was not suitable for buildings and bridges. The second was in his vertical integration of all suppliers of raw materials. In 1883, Carnegie bought the rival Homestead Steel Works, which included an extensive plant served by tributary coal and iron fields, a long railway, and a line of lake steamships. In the late 1880s, Carnegie Steel was the largest manufacturer of pig iron, steel rails, and coke in the