Since 2015, archaeological research carried outon the site of Soto (Kaffrine region, Senegal -L. Laporte and H. Bocoum, dir.) shed new light at funerary tumulistructures (Mbaanar) so far little studied. Among all acceptionsthe term Mbaanarcovers, many of them are materializedin the landscape by discretemounds of less than fifty centimetersin height. Very few exampleshave a frontal stone erected ontheireastside, as it is the case in Soto. On the eastern periphery of the tumulus, a protohistoric ground level is indicated by a crown of laterite gravel. A broad depression in its center indicates the initial location of the lyre stone. Extracted in 1964, this stone with central tenon is now exposed and integrated into the collections of the Musée du Quai Branly (Paris, France). Geophysical sur-veys conducted at Soto had highlighted a «clay anomaly» in the centerof the monument. This one is surrounded by a discontinuous peripheral ditch and some hollow structures. Extensive excavationsthen made it possible to revealthe entirety of a monumental earthen architecture of about 25 m in diameter and at least 1.5 m high. This oval-shaped monument iserected at thecenter of a large circular pit and issurrounded by several more or less continuous peripheral ditches. The structure of the monument testifies to an ela-borate architectural project and a mastery of mud construction techniques. A geoarchaeological study is actually in progress, in parti-cular to specify construction techniques and identify possible collapsed parts of the earthen architecture. His central part is made of a yellow earth core, probably surrounded by a palisade of about 10m in diameter whichmay have initiallycovered the funerarylevels. Then, several beds of raw earth placed at the top coverthe entire structure, appearing as many successive steps. On one of them, a spearhead had been planted vertically. For the first time in West Africa, this multidisciplinary work reveals a completely unsuspected monument in size and shapewhere many had previously seen only small sand hills. This somehow well-hidden ostentation is here associated with a more classic megalithic element, now exposed to the sight of millions of visitors.