525 William Penn Place (also known as the Citizens Bank Tower) was completed in 1951 for the Mellon National Bank and the U.S. Steel Corporation. At 520 feet (160 m) tall, it was the second tallest building in Pittsburgh until 1970, the third tallest until 1984. The building has 41 floors and approximately 950,000 square feet (88,000 m²) of office space.