This article, largely on the basis of in-depth research in archives in Lisbon, provides an account of the trading systems linking Delagoa Bay to its southern hinterland. Within this framework we argue that the role of the slave trade has been previously underestimated. There is evidence that the booming demand for slaves in Brazil and on the Mascarene Islands hit this region with force. The scale of that trade is difficult to establish because it was, by and large, illicit and so not systematically recorded. There are indications of a significant trade prior to 1823 and a substantial one after that date. There is also evidence that northern Nguni groups, including the Zulu kingdom, were deeply involved in this trading system. The main sources of captives, however, were militarily weak societies, like the Tembe, which lived closer to the Bay.