Since it is related by so many we can accept it
Ca da Mosto
There have been several accounts of the practice known as ‘silent trade’ in west Africa during the last thousand years. The oldest known account, that of Herodotus, is almost twenty-five hundred years old–although it probably refers to northwest rather than west Africa. Such accounts purport to describe exchanges of imported goods for gold from sub-Saharan Africa. These exchanges are said to have been made according to very particularized rules: two (and only two) trading parties would transact business with one another. They would do this not only without the help of middlemen but also without speaking to one another, or coming face to face or even within sight of each other. Elaborate precautions would in fact be taken to prevent any kind of direct visual contact. Despite this mutual avoidance and the resulting impossibility of negotiating rates of exchange, agreement presented no serious difficulties. Bargaining was carried out through gradual adjustment of quantities, arrived at by alternate moves by the two parties. Though each of the two in turn would have to leave his goods unguarded in a place accessible to the other, neither would take advantage of this for dishonest purposes. A shared table of market and moral values, as well as (and in spite of) silence and mutual invisibility, were thus the trademarks of such exchanges.
The available accounts may conveniently be grouped into two categories. One category represents the exchanges as taking place between traders coming from what are assumed to be ‘more developed’ cultures (e.g., Carthage or medieval north Africa) and ‘less developed’ barely known cultures outside the sphere of direct influence of the greater sub-Saharan pre-colonial states. The other category refers to contacts between those barely known cultures of the hinterland and black Africans (e.g., Wangara, ‘Accanists’) playing the role of middlemen between the gold producers and the Arabs and Moors or Europeans. It is on the information provided by these middlemen that the second category of accounts depends.