Ancient mounds in Louisiana that predate Egypt’s Great Pyramid are still puzzling scientists roughly 5,500 years after construction began.

Native American hunter-gatherers built the eleven earthworks at Watson Brake, near Monroe, around 3500 BC, nearly 1,000 years before the pyramid.

‘It is unclear why Watson Brake and other Middle Archaic mounds were built,’ archaeologist Rebecca Saunders wrote for the Louisiana Endowment for the Humanities.

The complex was mapped in the 1980s, but scientific dating in the 1990s revealed its remarkable age. Construction continued in stages for 600 to 700 years, with the builders connecting the mounds with ridges to create an oval enclosure roughly 1,000 feet across.

Using baskets, deer antlers and their bare hands, they raised eleven mounds without draft animals, a feat that likely required large groups working across generations. 

The tallest mound rises 25 feet above the surrounding ground.

The discovery helped overturn the belief that only farming societies could build large monuments, revealing that hunter-gatherers could organize and sustain major construction projects. 

Archaeologist Vincas Steponaitis, an expert in Native American mounds, said: 'It's rare that archaeologists ever find something that so totally changes our picture of what happened in the past, as is true for this case.'

Although identified decades ago, Watson Brake was featured in a video published by YouTube channel The Silent Ruins on September 10.

The mounds have long been hidden in a dense forest, but local amateur archaeologist Reca Jones recognized the earthworks after timber clearing exposed parts of the site in the early 1980s. 

She worked with Harvard graduate student John Belmont to produce the first map of the complex.

Researchers initially associated the mounds with the much younger Poverty Point culture, best known for another Louisiana earthwork complex built around 1700 to 1100 BC.

Investigations in the early 1990s by archaeologist Joe Saunders, soil scientist E Thurman Allen and colleagues revealed evidence that Watson Brake was considerably older.

Strongly developed soils suggested the earthworks had been weathering for thousands of years. 

The team used radiocarbon analysis and an independent technique called luminescence dating to investigate their age.

Radiocarbon analysis dates carbon-bearing remains such as charcoal, while luminescence estimates when mineral grains in sediment were last exposed to daylight.

The findings, published in Science on September 19, 1997, placed Watson Brake roughly 1,900 years before other then-known North American mound complexes with earthen enclosures.

A detailed study published in American Antiquity in 2005 reinforced the chronology using 25 radiocarbon dates and six luminescence dates.

Food remains show that the builders relied on fish, shellfish, deer, nuts and other wild plants, rather than cultivated crops.

Stone tools, beads and fired-earth objects offer clues about their daily lives, but the reason they devoted so much labor to the mounds remains uncertain.

One possibility is that construction helped bring scattered communities together.

'It could have been a way to reinforce relationships and cooperation,' Diana Greenlee, station archaeologist at Poverty Point and an adjunct professor at the University of Louisiana at Monroe, told Heart of Louisiana in an article published in 2022.

She also suggested that the earthworks could demonstrate a community's resources and ability to undertake major construction.

The 2005 study proposed that mound building may have been a communal response to droughts and flooding that made food supplies less predictable. That remains a hypothesis.

The mystery has parallels at Poverty Point, a separate Louisiana site whose main complex was built around 1700 to 1100 BC, centuries after Egypt's Great Pyramid.

Its largest mound stands 72 feet high and contains enough earth to fill roughly 31,000 modern dump trucks. A 2013 study suggested it was built in fewer than 90 days, possibly as little as 30.

In research published in 2025, Tristram 'T R' Kidder and colleagues proposed that Poverty Point was a temporary gathering place for trade, socializing and worship. 

They suggested mound building and offerings may have been a shared religious response to severe weather and flooding.

Those interpretations remain proposals, while Watson Brake's original purpose is still unresolved.

Watson Brake is not open to the public. Some of its mounds stand on privately owned land, although Louisiana has acquired part of the site for preservation.