In the early 1900s, archaeologist William Mills dug up a treasure-trove of carved stone pipes that had been buried almost 2,000 years earlier. Mills was the first to dig the Native American site, called Tremper Mound, in southern Ohio. And when he inspected the pipes, he made a reasonable—but untested—assumption. The pipes looked as if they had been carved from local stone, and so he said they were. That assumption, first published in 1916, has been repeated in scientific publications to this day. But according to a new analysis, Mills was wrong.