Stone Circles and Monoliths. The stone circles of the Senegal-Gambia region, dated circa 750, were produced to honor kings, chiefs, and perhaps other important individuals. Iron laterite (naturally cemented iron-filled sandstone), plentiful in this area, was the source material for these great stones. The numbers of stone circles are particularly high in this region, outstripping concentrations in other parts of the world. Stones number from ten to twenty-four per group or circle. Shapes of pillars are generally round, though some are square or rectangular, and others taper toward the top. There are also circles with V-shaped stones (known as lyre stones). Heights of stones usually remain the same within a particular circle. However, stones in different circles may range in height from twenty-four to ninety inches, in diameter from twelve to forty inches, and in weight up to ten tons. The...