Baggara genealogies claim that their origins go back centuries to connect with the Juhayna in the Hejaz before the days of the Prophet Mohammed. It is unclear how the Baggara reached their present areas. One theory suggests that after the Arab invasion of Egypt ( A . D . 1100-1200) the groups that became Baggara continued across North Africa to Tunisia, then came south across the desert into western Sudan. According to another theory, they were part of an invasion up the Nile Valley into Ouadaï and Bornu in the late fourteenth century. Throughout the centuries, there has been movement east and west. The Baggara, on the southern fringes of the sultanates of Darfur, Ouadaï, and Bagirmi in the west, and Al-Fung to the east, between the two Niles, moved east and west along the line of the sultanates according to their political fortunes. The Baggara retained access to goods and booty while avoiding payment of tribute. New tribes were added to the Baggara between the fifteenth and eighteenth centuries—for example, the Beni Khuzam and the Beni Helba. By the eighteenth century, the Baggara were concentrated to the east of Lake Chad, and north of Lake Chad in Darfur and Dar Ouadaï. At this period, some of the groups began moving eastward; first the Reizegat (into eastern Darfur), followed by the Messiriya, the Humr, and the Messiriya Zuruq, and the Hawazma. Cunnison (1966, 3) says that the Humr probably moved eastward from Ouadaï about 1775, and that by 1795 there were references to the Messiriya in the southwestern corner of what is now Kordofan. Baggara groups have become widely scattered, as a result of their lateral movement over the centuries. Although different groups tend to be concentrated in particular areas, territories are not as discrete as might be expected. There is some overlap and concurrent use of many areas. For example, the Hawazma and the Messiriya traverse much of the same territory, and they may, in the rainy season particularly, be found in adjacent camps. Kordofan and Darfur are characterized by great ethnic diversity and interdigitation; no group is wholly isolated or bounded from other groups. In the various regions, Baggara have close associations with camel nomads (Hamar, Shenabla), settled agriculturists (Nuba, Daju, Tungur, Bedayria, Gimaʿa, Zaghawa, Dar Hamid), and camel and sheep nomads (Maʿalia). Symbiotic relationships between herders and farmers are typical wherever pastoralists are found. In Kordofan, the relationship between the Hawazma and the Nuba is particularly significant. Traditionally, the Nuba were concentrated on and around the hills of the Nuba Mountains, rather than on the plains. Some Nuba groups claim to have always lived on the hills, whereas others moved up into the inaccessible areas as protection from Baggara raids and Mahdist troops. Whatever the case, the Hawazma and the Nuba represent an important example of symbiotic use of the same savanna ecozone. The Nuba are settled farmers who grow sorghum. They provide the Hawazma with some manufactured goods and with labor for both cropping and herding. For their part, the Hawazma provide animal products, milk, hides, and manure to the Nuba.