People gather at the ancient Serpent Mound earthwork in Peebles to celebrate the winter solstice in December 2014. [Dispatch file] ▲

Whenever I give presentations about the amazing earthworks built by Ohio's ancient American Indian cultures, a frequently asked question is, "How long did it take to build them?"

In a new article on architectural energetics, Jamie Davis, Jarrod Burks and Elliot Abrams show how to answer this question using Ohio's Serpent Mound as an example.

As a first step, they created a 3D model of the Serpent using drone imagery and gauged the mound's volume, arriving at 42,500 cubic feet.

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There is debate over whether the Adena culture built Serpent Mound more than 2,000 years ago, or whether the Fort Ancient culture built it around 1,000 years ago, but Davis, Burks and Abrams chose to focus on the Adena.

The Adena lived in small hamlets widely scattered across the landscape, each with 12 or so residents. To build something as large as Serpent Mound, people from many hamlets came together to share the labor.

The Adena built a few really big mounds, such as Miamisburg Mound, but they built them in stages over centuries. Serpent Mound was different. The evidence suggests it was built in a matter of days.

The Adena certainly could have done it. Assuming each laborer dug up and moved 60 cubic feet of earth per day, Davis, Burks and Abrams calculated that 259 people from 65 hamlets could have built the mound in "a five-day ceremonial event." But there is no evidence that the Adena ever built another animal-shaped mound or, indeed, any mound as large in such a short period of time.

What if the Fort Ancient culture built the Serpent? Davis, Burks and Abrams' model can be similarly used to estimate that number.

There was a Fort Ancient village next to Serpent Mound. An early archaeologist determined there were 20 houses there, which represent 140 to 260 people, with only about half of those able to contribute to mound construction; and those 70 to 130 workers could have built Serpent Mound within 10 to 20 days.

Building Serpent Mound was an extraordinary achievement regardless of who did it, but particularly so if it was the Adena. They had to get many widely dispersed hamlets to come together to build a one-off monumental masterpiece.

The Fort Ancient villagers, on the other hand, could have built Serpent Mound on their own. It's also worth noting that they built other animal-shaped mounds, such as Licking County's so-called Alligator.

Though archaeologists may never know for sure which group of people built the Ohio landmark, a tool like architectural energetics helps us understand the human labor costs behind such monumental architecture and contemplate scenarios' plausibility.

Brad Lepper is curator of archaeology at the Ohio History Connection.

blepper@ohiohistory.org