A research team that includes Edward Herrmann, a senior research scientist and geoarchaeologist within the College of Arts and Sciences’ Department of Earth and Atmospheric Sciences at Indiana University Bloomington, recently discovered evidence of an agricultural system dating back more than 1,000 years at the Angel Mounds State Historic Site.
Research spotlight: Department of Earth and Atmospheric Sciences
The 600-acre site in Evansville, Indiana, consists of 12 mounds inhabited by indigenous groups belonging to the Middle Mississippian culture from about 1100 to 1425 A.D. The team of archaeologists, earth scientists, and anthropologists published their findings in the Journal of Field Archaeology in September, add to a growing body of knowledge of indigenous cultures before Euro-American displacement.
In November 2020, Dr. Herrmann and Rebecca Hawkins from Algonquin Consultants were investigating a site intended to be used as a pollinator garden at Angel Mounds when they noticed something unusual: dark, linear furrows in the soil that had become buried underground over time. “At first, we thought these were just modern plow scars. I would’ve staked my reputation on that,” said Herrmann about the initial ground penetrating radar and magnetometry results. Further excavations, however, revealed that these furrows were significantly wider than modern plow scars.
Puzzled, the team considered other possibilities: were they trenches for building houses? There were no posts or building materials that would indicate construction. “We thought about a lot of things before we got back to ‘this might be agriculture after all,’” said Herrmann.
“Ed called somebody, and I called somebody and sent photos from my phone and said, ‘what do you think this is?’” recounted Hawkins. “Neither of us have ever seen anything like this,” she said.
Hawkins’ contact was quick to confirm the suspicion that the findings were evidence of ridge and furrow agriculture: a method in which a trench one to three feet wide is dug in the soil and piled to the side, forming successive rows of peaks and valleys.
The site’s location along the Ohio River made the site a key political and trade hub, and thus an important cultural site for the tribes who are currently affiliated with it: the Miami Tribe of Oklahoma, the Quapaw Nation, the Shawnee Tribe, the Eastern Shawnee Tribe of Oklahoma, the Absentee Shawnee Tribe of Indians of Oklahoma, the Peoria Tribe of Indians of Oklahoma, the Delaware Nation, and the Delaware Tribe of Indians.
Ridge and furrow agriculture has been used worldwide and was a common form of agriculture in Europe beginning in the Middle Ages, and for good reason. The farming technique helps protect crops from frost and pests, promotes soil irrigation, mitigates erosion, and more. But there was one problem: ridge and furrow agriculture had never been found this far south in Indiana.
Yet, the evidence grew. The team spoke to several specialists to determine if their findings were consistent with ridge and furrow agriculture. A paleoethnobotanist examined the remains of plants in the furrows and was able to identify that the types of plants grown there—beans, maize, bottle gourds—were domesticated species. At some point, someone had purposefully planted, cultivated, and tended these plants within the ridges.
August Costa (IU Ph.D. graduate of 2012), a geoarcheologist specializing in micromorphology, analyzed the sediment composition of the area. He found evidence that the soil within four furrow samples had been mechanically disturbed, perhaps by a hoe or other farming tool.
Herrmann noticed a similar pattern at the macro level. One day during the excavation, while digging in one of the furrows, Herrmann found irregular markings in the soil. “I was using a little tiny pick and brush, and [Hawkins] jokingly said ‘What are you doing? Are you trying to avoid work?’” remembered Herrmann. He carefully brushed away sediment to reveal what seemed like hoe marks left by someone tilling the soil.
Although the hoe marks may not seem all that surprising to find in cultivated soil, the discovery struck the researchers. “There is a little something that is just more personal about this finding,” said Hawkins, “you can imagine that someone stood right here and made this field.”
“It humanizes what we do,” agreed Herrmann.
Ridge and furrow agriculture systems are maintained by plowing or burning residual cultivars at the end of the season and piling their burned remains on top of the ridges. The team collected various samples of burnt plant material during the excavation of the furrows and used radiocarbon dating to determine that the cultivars had been grown at different times between 900 A.D. and 1800 A.D.
However, “I don’t want to suggest that there were 800 years of continuous agriculture,” cautioned Herrmann. Instead, the evidence points to three separate periods of use: around 900 A.D. prior to the Mississippian occupation, during the Mississippian period from 1100-1425 A.D., and in the late 18th and early 19th centuries, prior to the establishment of Euro-American farms in the area.
Since Angel Mounds is commonly described as a Mississippian cultural site, these pre- and post-Mississippian findings, “threw us right out of the bubble," said Herrmann. The researchers were particularly intrigued by plant samples dated to the early 19th century, which offer insight into agricultural practices of the inhabitants of Angel Mounds shortly before the arrival of Euro-American settlers in the early 1800s.
“Working for a tribe that was removed from that area and has real interest in that late time period when they were living there, the question is: what did life look like?" said Hawkins. Understanding the agricultural systems and the type of crops grown by indigenous groups in that time are a step towards answering that question.
Herrmann, Hawkins, and their collaborators plan to continue to explore the agricultural areas in and around Angel Mounds using the methods of ground penetrating radar and magnetometry described in their recent publication.
“The bottom line is, we’re confident this is not the earliest example of this kind of agriculture [in southern Indiana],” said Herrmann, “Archaeologists will find older [evidence] at some point, but now we have a template that might be helpful to look for it.”