Photo by Valentino Martinez

On this day in 1965, workers "top out" the final section of the Gateway Arch in St. Louis, Missouri, completing construction of the nation's tallest memorial.

A graceful 603-foot high ribbon of gleaming stainless steel, the Gateway Arch spans 630 feet at the ground and is meant to symbolically mark the gateway from the eastern United States to the West. Architect Eero Saarinen's dramatic design was chosen during a 1947 competition, and has since become a landmark famous around the world.

The Gateway Arch is the most prominent feature of St. Louis's Jefferson National Expansion Memorial Park, which also includes an Underground Visitors Center featuring exhibits charting the 100-year history of America's westward expansion. Although St. Louis was by no means the only jumping-off point for emigrants moving westward, during much of the 19th century the city's advantageous location, just below the confluence of the Mississippi and Missouri Rivers, made it an important hub for much of the nation's western expansion. Most famously, Lewis and Clark began their exploration of the newly acquired Louisiana Territory when they departed from St. Louis in May 1804, and Zebulon Pike also started his western explorations there in 1805. Once these famous trailblazers had shown the way, thousands of other followed in their footsteps.

For a time, St. Louis was also a center for the fur trade, as the mountain men scoured the western streams and lakes for valuable animals and sent their skins back East through the city. As the tide of easterners emigrating West steadily grew, St. Louis also became a popular jumping-off point for the main overland trails to Santa Fe, California, and Oregon. The arrival of the first steamboat, the Pike, along the docks of St. Louis in 1817 began the city's role as a hub for steam-powered water transportation along the Mississippi and Missouri Rivers.

Railroads, too, ensured that St. Louis would be an important transportation center for the second half of the 19th century. However, railroads also made it possible for the upstart city of Chicago to begin challenging St. Louis's role as the gateway to the West. With its easy access to the extensive network of eastern lakes, canals, and railroads, after 1850 Chicago began to supplant St. Louis as the major railway hub and economic center of the West.

http://www.history.com/this-day-in-history/workers-complete-the-famous-gateway-arch-in-st-louis-missouri