On October 28, 1965, construction is completed on the Gateway Arch, a spectacular 630-foot-high parabola of stainless steel marking the Jefferson National Expansion Memorial on the waterfront of St. Louis, Missouri.

The Gateway Arch, designed by Finnish-born, American-educated architect Eero Saarinen, was erected to commemorate President Thomas Jefferson’s Louisiana Purchase of 1803 and to celebrate St. Louis’ central role in the rapid westward expansion that followed. As the market and supply point for fur traders and explorers—including the famous Meriwether Lewis and William Clark—the town of St. Louis grew exponentially after the War of 1812, when great numbers of people began to travel by wagon train to seek their fortunes west of the Mississippi River. In 1947-48, Saarinen won a nationwide competition to design a monument honoring the spirit of the western pioneers. In a sad twist of fate, the architect died of a brain tumor in 1961 and did not live to see the construction of his now-famous arch, which began in February 1963.

Completed in October 1965, the Gateway Arch cost less than $15 million to build. With foundations sunk 60 feet into the ground, its frame of stressed stainless steel is built to withstand both earthquakes and high winds. An internal tram system takes visitors to the top, where on a clear day they can see up to 30 miles across the winding Mississippi and to the Great Plains to the west. In addition to the Gateway Arch, the Jefferson Expansion Memorial includes the Museum of Westward Expansion and the Old Courthouse of St. Louis, where two of the famous Dred Scott slavery cases were heard in the 1860s.

Today, some 4 million people visit the park each year to wander its nearly 100 acres, soak up some history and take in the breathtaking views from Saarinen’s gleaming arch.