The Neolithic civilization of the Senegal River valley and the Ferlo are the least well known due to not always being separated. Prehistory In the case of Senegal, the periodization of prehistory remains controversial. It is often described as beginning with the age of metallurgy, thus placing it between the first metalworking and the appearance of writing. Other approaches exist such as that of Guy Thilmans and his team in 1980, who felt that any archeology from pre-colonial could be attached to that designation or that of Hamady Bocoum, who speaks of "Historical Archaeology" from the 4th century, at least for the former Tekrur. A variety of archaeological remains have been found: On the coast and in river estuaries of the Senegal, Saloum, Gambia, and Casamance rivers, burial mounds with clusters of shells often referred to as middens. 217 of these clusters have been identified in the Saloum Delta alone, for example in Joal-Fadiouth, Mounds in the Saloum Delta have been dated back as far as 400 BCE, and part of the Saloum Delta is now a World Heritage Site. Funerary sites or tumuli were built there during the 8th to 16th centuries. They are also found in the north near Saint-Louis, and in the estuary of the Casamance. The West is rich in burial mounds of sand that the Wolof refer to as mbanaar, which translates to "graves", A solid gold pectoral of mass 191 g has also been discovered near Saint-Louis. In a huge area of nearly km2 located in the center-south around the Gambia there have been found alignments of boulders known as the Stone Circles of Senegambia which were placed on the list of UNESCO World Heritage sites in 2006. Two of these sites are located within the territory of Senegal: Sine Ngayène and Sine Wanar, both located in the Department of Nioro Rip. Sine Ngayène has 52 stone circles including a double circle. At Wanar, they number 24 and the stones are smaller. There are stone-carved lyre in the laterite, Y- or A-shaped. The existence of proto-historic ruins in the middle Senegal River valley was confirmed in the late 1970s. Pottery, perforated ceramic discs or ornaments have been unearthed. Excavations at thé site of Sinthiou Bara, near Matam, have proved particularly fruitful. They have revealed, for example, the flow of trans-Saharan trade from distant parts of North Africa. Kingdoms and Empires The region of modern