Both desert and grazing land, the Sahel has attracted a population as varied as its environment. Some are semi-nomadic cattle herders, moving with the seasonal flooding of the Niger. Others are farmers, eking out a living from millet and sorghum. The border with the Sahara is fluid and many of the people found in one region - the Tuareg and Hausa -- can be found in the other. But many groups owe their culture strictly to the Sahel. The Fulani, the word's largest group of nomadic herders, have long played an influential role in the region not only for their cattle, but for their advocacy of Islam. Their neighbors, the Dogon, practice a set of traditional beliefs that illustrate the power of the relationship between Africans and their environment.