Here are the latest developments in St. Louis' celebration of the Gateway Arch turning 50:

It's been a half century since the last, uppermost piece of the 630-foot-tall Gateway Arch went into place, and St. Louis is poised to observe that birthday.

Wednesday events include a morning Missouri History Museum remembrance by sheet-metal and iron workers, electricians and engineers who helped erect the wicket-shaped landmark that's St. Louis' famously defining feature.

A ceremony at 11 a.m. near the Arch will mark the moment 50 years ago that the final piece joined the nation's tallest man-made monument, along the Mississippi River's western bank. The city's mayor and National Park Service officials will speak.

And at noon, National Park Service historian Bob Moore joins landscape architect Susan Saarinen — daughter of the Arch's late designer, Eero Saarinen — for a panel discussion.