They are millenary structures and appeared in the USA. The 11 thousand year old mounds in Louisiana reach 6 meters in height. They are at the north end of the Louisiana State University (LSU) campus. Their age has now been determined with great precision.
Layers of clay and ashes of burned reed and rush plants were checked in their structure. Also microscopic fragments of animal bones. It is believed that the mounds were built and used for religious or ceremonial purposes.

Older than the pyramids
Mound B, farther south, is the older of the two. By radiocarbon dating, they determined that it is 11,000 years old. Mound A is about 7,500 years old.
This makes Mound A the oldest man-made structure in North or South America. Both mounds are even older than the ancient Egyptian pyramids. The oldest pyramid was built at Saqqara about 4,700 years ago.
A general chronology of the construction of the mounds was made. Mound B was probably built with material from that area beginning about 11,000 years ago. Over thousands of years, ancient humans continued to build. They used clay and burned plants and animals in the mound.
About 8,200 years ago, Mound B was abandoned. Climate change is likely to have been the cause. At that time temperatures in the northern hemisphere dropped by about 20 degrees Celsius.

Aligned to the stars
“We don’t know why they abandoned the mounds about 8,200 years ago. Their environment changed suddenly and drastically. It affected their daily lives,” said Brooks Ellwood, professor emeritus of geology and LSU.
There is no evidence of human activity at Mound B for the next 1,000 years. About 7,500 years ago, ancient people began building Mound A. They used mud from a floodplain.
The 11,000-year-old Mounds in Louisiana have a stellar feature. They line up just 8.5 degrees east of north. There the red giant star Arcturus would have risen several thousand years ago, according to astronomers. The research was published in the magazine American Journal of Science yale University.