The Upemba depression sells iron and salt up the Congo rivers

By the early centuries CE the country around the Upemba depression, where the Lualaba River runs through southern Congo, had become a serious industrial district. It produced iron, iron goods and salt, and shipped them north along the Lualaba and the Lomami into the trading networks of the central Congo basin. Then the region added a second metal. Ironworking Bantu communities living to the south, at the edge of the basin, sat on top of the copper deposits of southern Congo and northern Zambia, the ground later called the Copper Belt, and they worked out copper smelting for themselves. Nobody taught them. Copper then moved out in both directions, north up the rivers of the Congo basin and south through the Zambezi. Three commodities, iron, salt and copper, produced with African technique and carried on African rivers, supplied a continental market. The system was working while Rome still stood, and no standard account of the ancient world mentions it.

By around the third century CE the Malagasy speaking community on the East African coast had lived among Bantu speaking neighbours long enough to have married into them. Some of them then sailed south, crossed the Mozambique Channel, and settled Madagascar. What they carried was a working farm system assembled out of two hemispheres: African livestock and African grain beside rice, bananas and chickens from Island South Asia, together with the practices that belonged to each. Madagascar has been that combination ever since. Its people speak an Austronesian language whose nearest relatives are in Borneo. They raise cattle bred in Africa and poultry domesticated in Southeast Asia. They grow African sorghum in the same country as Asian rice. Their ancestry is Bantu and Austronesian together. The island is the clearest surviving record of how far the ancient Indian Ocean trade reached and what it did on arrival, which was to move people, crops, animals and languages until two ends of the world were permanently joined in one place.

The Council of Nicaea met in 325 CE to settle what Christians were required to believe about the nature of Christ. The argument was carried by Alexander, the Egyptian patriarch of Alexandria, and by his student Athanasius, who between them defeated the position that Christ was a created being. Out of the council came the doctrine of the Trinity and the statement of belief still recited as the Nicene Creed. Every later century of Christian theology in Europe was built on that foundation, and it was fixed in place by two men from Egypt. The other decisive figure of the period was also African. Augustine was born in the fourth century at Hippo, in what is now Algeria, of Amazigh descent, and his writing on sin, grace, predestination and the standing of the church shaped Catholic doctrine for sixteen hundred years and handed the Protestant reformers their arguments as well. He learned his trade inside an African intellectual tradition that had already produced Tertullian and Cyprian.

Textbooks teach a sequence for metals in which copper comes first and iron follows long after, because that is how it went in Europe and the Middle East. South of the Sahel the order runs the other way. Iron smelting was established across two thirds of Africa before copper was worked at all, and knowing how to hold a furnace at heat is what led people to recognise copper ores and smelt them. The clearest case is the belt of copper rich country running from central Zambia into the southern Congo. Bantu speakers of the Sabi group began working those ores no later than the fourth century CE, several centuries after iron reached them. Copper and copper goods then moved out along the Zambezi watershed and up the rivers into the Congo basin. From about the eighth century a further set of Bantu communities spread through the same region, their speech ancestral to the Luba dialects heard there now, and the older Sabi language fell out of use while the mines kept growing.