On October 28, 1965, Topping Day, the last piece of the arch is set into place. Fireworks shoot over the Gateway Arch to celebrate the 50th anniversary of its completion on Saturday, Oct. 24, 2015. This Wednesday is the official day the final piece was placed in 1965. ST. LOUIS • The Gateway Arch will be splashed in gold floodlight Wednesday for the golden anniversary of “topping day” 50 years ago. Free events are planned downtown and at the Missouri History Museum in Forest Park.