Serpent Mound, near Peebles in southern Ohio, is a prehistoric effigy earthwork stretching 1,348 feet along a bluff above Ohio Brush Creek, making it the largest known serpent effigy in the world. Shaped as a winding snake with a tightly coiled tail and a head reaching toward an oval earthwork, it has inspired debate over both its meaning and its builders. Recent research has argued for Adena construction around 300 BCE with later Fort Ancient rebuilding, while other archaeologists attribute it to the Fort Ancient period instead. Preserved beginning in 1886 and designated a National Historic Landmark in 1966, it remains a major monument of pre-contact North America.