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Cahokia Mounds State Historic Site

BACK in 2015, I stood in a grassy field in southern Illinois, looking at a map of the 1000-year-old neighbourhood buried right beneath my feet. Nearby, cars drove by on a narrow road and a group of squat fuel tanks cast long shadows in the early morning sun. The place looked like the outskirts of a typical farm town, but the two archaeologists with me had uncovered something that couldn’t be seen with the human eye: not far below the ground were some shadowy blobs, arranged in a circular pattern.

Sarah Baires is an archaeologist …