By 1900, downtown Pittsburgh, known as the Golden Triangle, had become a classic central business district at the confluence of three rivers: the Allegheny, the Monongahela, and the Ohio. The valleys of the three rivers were lined with the factories and mills that made Pittsburgh the "forge of the nation." Great industrialists such as Andrew Carnegie and George Westinghouse made Pittsburgh the center of the American iron, steel, aluminum, glass, and oil industries. With their success, money poured into Pittsburgh's banks, providing means for the city's growth. The years between 1900 and 1945 witnessed the peak of Pittsburgh's commercial development and industrial might. Pittsburgh: 1900-1945 features postcard views taken during this period and illustrates the power, wealth, and beauty of the city of Pittsburgh during its era of industrial greatness.