Higher Ground: America's Mound Builders · Episode 5 of 7 · 35 min
The DaVincis of Dirt: The Lost Soil Science of Monks Mound
How do you build a hundred-foot mountain of wet dirt that does not wash away in a thunderstorm? Monks Mound holds some 22 million cubic feet of earth and stood for a thousand years. The episode digs into the builders' geo-engineering: selectively mined soils, waterproof clay veneers, sand-drained layers, sod blocks stacked like sandbags, and rapid construction. The mounds began to slump only after modern engineering upset the water balance they had designed.
Who's who
- Tristram R. KidderWashington University geoarchaeologist; co-author of 'The DaVincis of Dirt'
- Sarah C. SherwoodGeoarchaeologist and co-author of 'The DaVincis of Dirt'
Where it happens
- Monks Mound, Cahokia, Illinois+1 more episodeLargest pre-Columbian earthwork north of Mexico
- Poverty Point, Louisiana+3 more episodesSelectively mined pure soil and rapid building
- Shiloh Mound A, TennesseeRed clay veneer and pore-pressure-balanced fill
Timeline
- c. 1700-1100 BCEPoverty Point's Mound A is raised apparently within months.
- c. 900-950 CEConstruction begins on what becomes Monks Mound.
- c. 1100 CEMonks Mound reaches roughly its finished four-terrace form.
- c. 1250 CEShiloh's Mound A receives a prepared red clay veneer.
- c. 1956Modern slumping begins after groundwater reduction dries the interior clays.
- 2011Kidder, Sherwood and colleagues publish 'The DaVincis of Dirt.'
Still debated
The classic estimate of a thousand laborers over ten to twenty years competes with newer readings that compress construction into a few decades. How general the engineering techniques were across mounds is also uncertain.
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