On the floor of the Great Mound, they placed two “great deposits” of objects, many of them ritually broken, and burned. Even after two thousand years underground, their beauty and astonishing variety are still clear today. There are some sharp contrasts, or dualities, here: All the obsidian, for instance, was in the eastern deposit; all the pearls in the western one.

Two deposits, left under a small mound here near the bluff, were also deliberately different from each other: all the mica was in one, on a square tablet; while all the copper was in the other, on a round disc. To those who left them, the dual deposits probably seemed like two parts of a whole. These signs of unity were placed among the burials, but not connected with any particular ones. They suggest the variety of ceremonies that took place, in the buildings, later memorialized by mounds.

Sometimes, mounds covered extraordinary deposits of unworked materials. At Mound City, for instance, Mound Five was built over a fire basin, filled only with thirty pounds of galena – lead sulfide, which they left in its shiny, crystalline form. At the Hopewell site, there were mounds dedicated to mica slabs, and to obsidian pieces.

Another mound held over eight thousand flint discs, laid down carefully in two layers, and set in fine gravel. They were in little bundles, each about as many as one person could carry. Why were these materials left like this? Were they reserves, for use in another world? Offerings made to people, or spirits? Or some form of thanks to the earth, for its gifts? Whatever their meaning, these deposits show how much the people valued the rare materials from which they shaped their most precious objects.