High Quality Content by WIKIPEDIA articles! St. Louis, Missouri is the 58th largest city in the United States and has the 89th most impressive skyline in the world, according to rankings by Emporis. The tallest accessible structure in St. Louis is the 630-foot (190 m) high Gateway Arch, which was completed on October 28, 1965. It also stands as the tallest monument in a National Park, rising 75 feet (23 m) higher than the Washington Monument (and still shorter than the San Jacinto Monument, 567 feet, Houston Ship Channel in Texas), and is the tallest accessible structure in Missouri. The tallest habitable building in the city is the 42-story One Metropolitan Square, at a height of 593 feet (181 m), which was completed in 1989. It was designed by architecture firm Hellmuth, Obata & Kassabaum (HOK), which is also headquartered in the building. It is the second-highest building in Missouri and the tallest habitable building. HOK has also designed several other skyscrapers in St. Louis, including One AT&T Center and the Thomas F. Eagleton United States Courthouse. As a result, the only three habitable buildings in St. Louis over 500 feet (150 m) tall have been designed by HOK. However, no buildings in Missouri are over 700 feet (210 m) and are therefore not among the tallest buildings in the United States.