Buried beneath today's Midwestern towns, under several layers of earth and the accumulated debris of two thousand years, are the clues to an ancient mystery. A Native American people, now known as the Hopewell, lived and worked these lands, building earthworks which in some instances dwarf the ruins at Stonehenge. More significantly, these mammoth earthworks were built in different geometric shapes, using a standard unit of measure and aligned to the cycles of the sun and the moon. Using the foundation of existing scholarship, this book presents new discoveries showing the accomplishments of the Mound Builders in astronomy, geometry, measurement, and counting. William Romain then goes one step further to theorise why generations of people toiled to move millions of tons of earth to form these precise structures, joining the ranks of the Egyptians, Mayans, Greeks, Chinese, and other advanced ancient cultures. This book will appeal to many readers, including anthropologists, mathematicians, and historians, but perhaps especially to readers curious about ancient cultures and seeking explanations for these magnificent earthen structures.