Sub-Saharan Africa is the ancestral home of millions of Americans and, according to some anthropologists, the cradle of mankind-the birthplace of Homo sapiens. From at least the first millennium B.C., elements of Egyptian, Phoenician, Greek, Roman, and Arab culture spread southward into Africa through conquest, trade, and the dissemination of Christianity and Islam. Trade in slaves, gold, copper, salt, spices, and many other items flourished both by sea and, following the introduction of camels in about the third century A.D., across the Sahara.