The Whistler Mound Group and Enclosure originally consisted of 70 conical or round burial mounds and a low, earthen double enclosure. The site has never been scientifically investigated, so the exact date of construction is unknown. Archaeologists believe the mounds were constructed during the late period of mound building, circa 650~1200 A.D. Enclosures like this one were once found throughout the northeastern United States. Their function is not known, but they are thought to define sacred space where special ceremonies were conducted. The Whistler enclosure is one of the few in Wisconsin to have escaped destruction by modern development. Most mounds in Wisconsin have been destroyed. The remnants of the Whistler Mound Group and Enclosure are now protected by Wisconsin's burial law and the site was listed in the National Register of Historic Places in 1993.