Mound-builder societies produced functional and graceful structures, including the Great Serpent Mound in the Ohio Valley.
Circa 500 CE, mounds such as the one above show remains of walled complexes with community plazas, woodhenge (think Stonehenge but with wood) and 10 storey high structures, the likes of which required moving more than 1.5 million cubic metres of earth to build.
Also Cahokia probably served as a centre for regional commerce long before Columbus' maiden voyage.