The Bamana harness supernatural energy (nyama) to resolve disputes, cure illnesses, hunt down witches and other negative spiritual forces, and to generally protect the community from harm. To help harness nyama, boliw (sing. boli) figures are created to house the energy of these supernatural forces—boliw are believed to be physical manifestations of nyama. The most sacred of all Bamana sculptures, these ritual objects are handled only by a select group of seven to eight elders who have political authority over the Bamana community. To activate the boli, sacrifices of animal blood and food offerings are 'fed' to the figure. According to Sarah Brett-Smith: "Symbolically boliw may be viewed as stomachs which are ritually “fed" and kept within the association's belly (the sacred grove), the place where Kono eats".3
Once charged, boliw figures are believed to be supernatural judges, presiding over community disputes. The elders in charge of the boli, consult it for its judgment and announce the ruling issued down by it. In essence, the boli is judge, jury, and executioner. Boli figures are also believed to bring prosperity to a community; they ensure fruitful harvests and increase the fertility of the land and its women.
Each community has at least one boli figure but it's not uncommon to see a 'family' of boliw in a given village: the largest boli—'the father of the children'—is called boli den fa and the children are called boli denw.