Discover the Oldest Human-Made Structures in the US That Date Back to 9000 B.C.

Discoveries constantly change how people see history. Every time historians think they’ve gotten everything figured out, they find something else that changes everything. Take the oldest human-made structures in the US for example.

For a while, the oldest structures were thought to be from 3500 B.C., but newer studies from 2022 have shown that there are some places in the US that date back to over 9000 BC.

To learn more about these structures, including their location, continue reading below.

Where Are the Oldest Human-Made Structures in the US?

You might expect the oldest structures in the United States to be somewhere deep in the woods, far away from civilization. However, you’d be quite wrong.

The oldest structures in the US that date back to 3500 B.C. are located in the heart of Baton Rouge, Louisiana. To be more specific, the two structures that are currently considered the largest human-made structures in the U.S. are on the north side of Louisiana State University’s (LSU’s) campus.

What Are the Oldest Human-Made Structures in the US?

If you’ve ever been to LSU’s campus before, you’ve likely seen the two mounds on the north end. They are rather out of place and stand out amongst the flat land surrounding them. They are named Mound A and Mound B.

However, while many people might have just put down the mounds as some sort of strange decorative choice by the campus, there’s actually something much more interesting going on.

These mounds were made by people. For a long time, scientists knew that these mounds were human-made and old. However, no one ever expected how old they were. Once studied, scientists found that the oldest mound dates back to over 11,000 years ago.

History of the Mounds

There’s a lot of unknown information about the mounds, but scientists are starting to piece it together. It’s thought that Mound B was used for thousands of years. Then, about 8,200 years ago, the mound was abandoned.

Though scientists don’t entirely understand why, it is known that about that long ago, the temperatures dropped by about 35 degrees Fahrenheit and stayed that way for about 160 years. People either had to flee the area, or adjust to the cold. In this case, it seems that the people chose to flee.

Then, 7,500 years ago, people came back. One of the first tasks they did was to build a second mound. Mound A is only about 30 feet away.

During their research, scientists discovered something else interesting about the mound. Both aligned towards a red star called Arcturus. When you stand where the mounds are aligned, it is in the same direction where the star rose in the sky during that time in history.

The Purpose of the Mounds

When studying the mounds, scientists discovered that at the core of each mound were layers of clay, ash, plants, and bone fragments.

Based on the plants burned, reed, and cane, it’s thought that the mounds must have had ceremonial or religious use. Canes and reeds aren’t often used for cooking because they burn too hot.

The Discovery of Watson Brake

There is no clear day to pinpoint when the mounds were first discovered, as they have been there since before people from Europe even landed in North America, and even before there was a Europe. On September 19th, 1997, the oldest man-made structures in North America were found in Watson Brake, Louisiana. They were dated back to 5,400 years ago. This made them 2,000 years older than other mounds in the area.

The mounds are found from Louisiana to Florida. Even this discovery dating back to 5,400 years ago was enough to completely rewrite North America’s history. Finding ones over 11,000 years ago has further altered what historians thought happened in North America in the past.

While the oldest structure dates back to 9000 B.C., not every mound does. Even the two mounds next to each other on LSU’s campus have the same date. The southernmost mound, named Mound B, is older than the other mound, Mound A.

While Mound B dates back to 11,000 years ago, Mound A only dates back to 7,500 years ago. Though there’s quite a difference in age between the two hills, they are both still old. In fact, both are older than the pyramids from Ancient Egypt. Even the oldest pyramid, considered to be the Pyramid of Djoser, was only constructed 4,700 years ago.

The photo featured at the top of this post is © Philip Rozenski/iStock via Getty Images