Silent trade

Silent trade, or barter, is when traders (who do not speak each other's language) trade without talking to each other. This was used in many parts of ancient Africa. Silent bartering was used during 500 A.D to 1500 A.D. and probably had a much longer history.
To do a silent barter, one group of traders would go to a certain place, leaving whatever they are offering to trade. The other group of traders would then decide if they would like to accept the goods (usually salt or gold) that were left. If the goods met with approval, the second group would then take the goods, leave their own goods in return, and leave because the person accepted the offer. This system of trading was used mostly in ancient Ghana. The popular things they sold were gold and salt. Another system was face-to-face trading using hand signals.
Gold mined south of the Sahel was traded, pound for pound, for salt mined in the desert. The salt from the desert was needed by the people of Sahel to flavor and preserve their food and gold has always had value for adornment (wearing). Because of this trade, cities grew and flourished and parts of West Africa became commercial centers. West Africa produced gold until about 1500 AD.