LiDAR reveals 50-ft earthen pyramid at Emerald Mound, Illinois near Cahokia

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Key facts

• LiDAR imagery made by LiDAR America shows an earthen pyramid at Emerald Mound in St. Clair County, Illinois, standing about 50 ft tall and covering roughly 300 by 300 ft (about two football fields).
• Emerald Mound lies about 15 miles from Cahokia and is considered one of the major cities of the Cahokia-centered Mississippian polity.
• The site is on private farm land, concealed beneath tall trees, so it is largely invisible in conventional aerial photography.
• An 1881 illustration of the mound calls it the 'Old Farm Mound'.
• Archaeologist Tim Pauket studied the site and estimates it spans 145 acres, with multiple temples, plazas and sweat lodges - more than a simple village site.
• LiDAR also shows a second earthen pyramid about 30 ft tall standing outside the main mound view.
• The site dates to about 1050-1350 AD, beginning with Cahokia's rise and outlasting Cahokia's abandonment in 1250.
• The video notes that some sources report the mound is oriented to the 18.6-degree lunar maximum, but says it has yet to see an archoastronomer confirm this.
• Despite being on private land, Emerald Mound was listed on the National Register of Historic Places in 1971.
• The LiDAR survey covered five virtually unknown earthen pyramid sites on private land across the United States.

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