This unique geometric shape is unknown anywhere else in Ancient America. The word "quatrefoil" refers to a symmetrical shape made by combining identical sections of four circles, a form that appears in the art and architecture of other global cultures. Although the Hopewell were masters of complex geometry, Junction's quatrefoil is entirely unique among their many geometric earthworks. When surveyors first recorded it in the 1840s, they thought it was a small, rounded-off square, but magnetometry surveys made here since 2005 revealed its more complex shape, and the quatrefoil was the new data's biggest surprise. Its three-part arrangement, with two adjoining circles, may prefigure the far larger three-part geometric enclosures built in the following centuries nearby. Five of these tripartite earthworks stood within fifteen miles, with the Seip Earthworks the best preserved, and all five were designed with the same three geometric shapes: a square, a circle, and a larger circle, with each figure enclosing the same number of acres at every site.