Initially this structure in Mauritania was thought to be an impact structure. It is now believed to be an eroded salt dome, but how it was formed is inconclusive. It is 50 km in diameter (23.5 km largest inner ring), about the size of modern city.
Besides this structure’s mysterious geological origins, it has been proposed by some that this structure closely resembles Plato’s ancient description of Altantis with its large concentric circular rings, and it really does match Plato’s description of Atlantis. It is also located in a region in Mauritania south west of the Pillars of Hercules (Strait of Gibraltar) below the Atlas Mountain range (“Atlantis” mountain range?).
It has been proposed by some researchers that Atlantis existed in the Antediluvian era, in a time before the Great Flood and the prehistoric ancient world’s destruction, and that it was destroyed by the Great Flood in a giant tsunami. It is also possible that parts of the ancient Sahara Desert were ocean. The structure itself does contain salt implying a dried up ancient sea. Perhaps the Mediterranean Sea spilled into the Sahara Desert during or prior to the last ice age, and that water subsequently spilled into the Atlantic ocean. Or it’s possible the land elevations in the past were very different than they are today. There also appears to be on main “channel” or “canal” leading away from the structure, which matches Plato’s description also.
One research has suggested that if this isn’t Atlantis itself, that it is perhaps an ancient city belonging to Poseidon’s ancient empire collectively called Atlantis, which later changed phonologically to “Atlantic”, where Poseidon was a king, not a god.
(Image owner: https://commons.wikimedia.org/wiki/File:ASTER_Richat.jpg)
The following is the only free movie linking the Richat Structure to Atlantis:
http://www.gpofr.com/documents/2012Atlantis.pdf (broken link 2014)