Bantu is the collective term describing more than 400 different ethnic groups in south and middle Africa. The Bantu languages are a sub-group of the Niger-Congo languages. Today (2007) more than 200 million people are Bantus. The Bantu likely come from the highlands of Cameroon and the southeast of Nigeria. At some point in the second millennium B.C., they began to extend their territory into the rain forests of central Africa, as planters of root crops. Around 1,000 years later, a second and more rapid phase of expansion began, this time to the south and east. Everywhere they went, they intermarried with the indigenous groups and formed new societies. Approximately 1000 B.C.–likely without any outside assistance– the skill of mining and smelting iron had been developed throughout the region between Lake Chad and the Great Lakes of East Africa. When the Bantu took on this technology, the settled region had already expanded considerably. They planted cereals and bananas and herded animals. The Urewe Culture of present-day Uganda is considered to have been the first early Iron Age culture of the Bantu. South of the Equator, the beginning of the Iron Age is considered to coincide with the arrival of the Bantu.