In the past, as today, no society was completely self-sustaining, and money allowed people to interact with other groups. People used different forms of currency to mobilize resources, reduce risks and create alliances and friendships in response to specific social and political conditions. The abundance and nearly universal evidence of movement of exotic goods over diverse regions inhabited by people who were independent of each other – from hunter-gatherers to pastoralists, to farmers and city dwellers – points to the significance of currency as a uniting principle. It’s like a common language everyone could speak.

For example, Americans who lived in the Early Formative Period dating from 1450 to 500 B.C. used obsidian, mother-of-pearl shell, iron ore and two kinds of pottery as currency to trade across the Americas in one of the earliest examples of a successful global trade. The Maritime Silk Road trade, which occurred between A.D. 700 to 1450, connected Europeans, Asians and Africans in a global trade that was both transformational and foundational.

In my own excavation work in 2012, I recovered a 600-year-old Chinese Yongle Tongbao coin at the ancient Kenyan trade port Manda, in the Indian Ocean. Chinese coins were small disks of copper and silver with a hole in the center so they could be worn on a belt. This coin was issued by Emperor Yongle of the Ming Dynasty. He was interested in political and trade missions to the lands beyond the South China Sea and sent Admiral Zheng He to explore those shores, nearly 80 years before Vasco da Gama reached India from Portugal.

Archaeological discoveries like this one illustrate Africa’s integration into trade interactions in the Indian Ocean. They also show evidence that market economies based on cash money were developing at this time. On the East African coast, there were local merchants and kings of the local Swahili who followed Islam and cultivated these external contacts with other Indian Ocean traders. They wanted to facilitate business dealings, while merchants from the Near East and South Asia had their own Rolodexes of business contacts. Coinage was not just a local affair but also a way of leaving a calling card, a signature and a symbolic token of connections.

As the history of money has shown, currency’s impact is double-edged: It enabled the movement of goods and services, migration and settlement amongst strangers. It brought wealth to some, while hastening the development of socioeconomic and other distinctions. The same patterns unfold today with the modern relationship between China and Africa, now more intertwined and unequal than when Admiral Zheng He first brought coins from China in a diplomatic gesture, as a symbolic extension of friendship across the distance separating the two.

In our time, possession of cash currency differentiates the rich from the poor, the developed from the developing, the global north from the emerging global south. Money is both personal and impersonal and global inequality today is linked to the formalization of money as a measure of societal well-being and sustainability. Even as currency continues to evolve in our digital age, its uses today would still be familiar to our ancient predecessors.