The Congo basin built a second African trade network by boat

West Africa was not alone. In the Congo basin, in the middle of equatorial Africa, a second network of long-distance exchange took shape within a few centuries of the first. Its main routes were the rivers. Traders from Bantu-speaking farming and fishing communities moved goods upstream and downstream by boat along a system of waterways that reaches most of the basin. Feeder routes ran through the rainforest to the landings, and along those tracks the Batwa foraging peoples carried hides, ivory, beeswax and honey out of the forest and into the river trade. The design follows the country. The Sudan belt used donkeys and open savanna; the Congo used canoes and rivers. Savanna towns sold manufactures; the forest network sold what the forest produced. Underneath both lies the same ordinary impulse to specialise, exchange and grow rich by moving what other people want. Most world histories have not yet registered that the Congo system existed at all.

Late in the Archaic Age the traffic grew heavier between the islands and the Isthmo-Colombian mainland of Central and South America. Goods moved, and so did people and ideas. Keegan and Hofman describe these routes as lifelines running back to the communities the islanders had come from, which is a precise way to put it. A small population scattered across islands needs contact to stay viable, socially and culturally and in the plainest biological sense, and the mainland connection supplied it. The archaeology of the period looks different from one island to the next, and the authors read that variation as people adjusting to the particular place they had landed in. What this era built was the framework the later ceramic age villages would use. The settled farming communities that eventually filled Hispaniola did not appear out of nowhere. They inherited routes, relationships and habits of movement that had been in service for centuries.

The spread of the early iron smelting sites carries two implications. The first concerns place. The pattern of the distribution makes it likely that the people who worked out the technology lived somewhere in the fifteen hundred kilometres of woodland savanna between central Nigeria and the far northwestern fringe of East Africa. The second concerns time. Sites were already scattered across that enormous stretch three thousand years ago, and a technology takes generations to travel that far, so the founding workshops should date centuries before 1000 BCE. Both expectations have since been tested. In the last two decades archaeologists have found earlier African ironworking than anything previously recorded, and the finds sit inside the predicted zone. Ôboui, in the western Central African Republic, is one of them. This is the pattern that keeps repeating in Ehret's field. A prediction is made from vocabulary and distribution, someone digs in the indicated place, and the dates come back older than the standard account allows.

Words for iron and for the work of the forge spread eastward across central Africa until they stopped in the west of South Sudan, along what is now the Ethiopian border. They stopped because another body of ironworking terms was coming the other way, southward out of the northern Ethiopian highlands. The two met in eastern South Sudan around the middle of the first millennium BCE. Each set carries its own words for the furnace, the smith and the tools, and each traces back to a different chain of transmission, one African in origin and one reaching the highlands from the Middle East across the Red Sea. Had iron been born once in Anatolia and radiated outward from there, the vocabulary across this whole region would descend from a single root. Instead there are two lexical systems running into each other from opposite directions, thousands of kilometres from where either began. That meeting place is where the single origin theory stops working.