Spread across a region 30,000 km2 (12,000 sq mi),[2] they are sometimes divided into the Wassu (Gambian) and Sine-Saloum (Senegalese) circles, but this is purely a national division.

The monuments consist of what were originally upright blocks or pillars (some have collapsed), mostly made of laterite, with smooth surfaces.

[6] Archaeologists have also found pottery shards, human burials, and some grave goods and metals around the megalithic circles.

[7] The construction of the stone monuments shows evidence of a prosperous and organized society based on the amount of labor required to build such structures.

After extracting the stone, identical pillars were made, either cylindrical or polygonal, with averages at two meters high and weighing seven tons.

The builders of the monuments here possessed great knowledge of their local geology in order to find the sources of laterite stones.

[10] The most recent excavations conducted on these megalithic circles date to the Anglo-Gambian campaign led by Evans and Ozanne in 1964 and 1965.

[2] A dating program has yielded estimates that place the construction of the double circle to between the twelfth and thirteenth centuries AD.

For instance, the inner ring of the double circle features fallen monoliths that fan out from the center of the monument.

This theory is not refuted by the fact that the stones of the outer ring fell in all different directions, lacking outward pressure.

[11] They also found evidence of hundreds of homes nearby, dating from around the time of the monuments, clustered in groups of 2–5, with remnants of house floors and pottery shards.

Researchers have also suggested the possibility that these megalithic cemeteries could have been a focal spot of the cultural landscape and served the purpose of bringing people together.

[17] The site of Sine Ngayène has a Y-shaped central axis, with a double circle (called Diallombere) located at the center of the three branches.

These cycles are based on materials buried in successive layers and the monument construction chronology of the double circle at the center of the site.

The main finding for this cycle was a large, oblong-shaped pit with a concentration of human remains in the form of a secondary burial.

[24] The majority of findings from this zone were small bone fragments buried with laterite blocks, located primarily in the inner circle of the monument.

There were also some sherds found in one spot, and a secondary burial pit containing 70 bones, seven turquoise beads, and two copper rings.