At the top, if you climb the maintained trail to the first terrace, you can see the Grand Plaza spread out below — the flat expanse that required the movement of millions of cubic feet of earth to create, that was the setting for the ceremonies and gatherings and public events that gave meaning to the city’s life.

Beyond the plaza, the American Bottom extends to the horizon, the flat floodplain of the Mississippi dotted with the shapes of surviving mounds and interrupted by the geometries of modern agriculture and urban development.

On a clear day, the arch of the Gateway to the West rises above St.

Louis to the southwest.

It is a monument to American expansion westward — to the opening of the continent to the United States’ growing population.

It stands approximately 13 miles from Monks Mound, and it is roughly the same height.