A currency of sorts was first thought to emerge as trade and exchange, with trade being tracked through the archaeological record, starting in the Upper Palaeolithic, when groups of hunters traded the best flint weapons and tools. Throughout the years, various objects were used as units of value until nearly 5,000 years ago, when the Mesopotamian shekel emerged as the first known form of currency.

Now, researchers from Leiden University in the Netherlands are adding an Early Bronze Age piece to the currency puzzle. They’re proposing that Bronze Age people may have used rings and axe blades as an early form of standardised currency. 

“Archaeology can provide a unique perspective on the development of money and systems of weighing over space and time, but the discipline has difficulties with the identification of objects that functioned either as commodity money or as weights,” the authors write in their paper, published in the journal PLOS ONE.

The authors compared objects from Early Bronze Age Central Europe. Based on the similarity in weight and shape of the objects, they suggest that ancient people used bronze objects that were standardised in shape and weight as currency. 

“Found in bulk, sometimes in hoards containing multiple hundreds, many of the rings, ribs and axe blades are considered to have no other practical function besides their tentative use as ingots, or rough-outs for further production,” the authors write. 

“Moulds, made of clay, stone or casted directly in sand made serial production possible, which led to some degree of unintentional standardisation. However, there are indications that for some types of objects, a deliberate effort was made to achieve a specific weight interval, meaning that weight mattered.”

The researchers studied just over 5,000 objects made of bronze in rings, ribs and axe blades from more than 100 ancient hoards.

The objects’ weights were compared using a psychology principle known as the Weber fraction, which suggests if objects are similar in mass, a human being weighing them by hand can’t tell the difference. 

Around 70% of the rings were similar enough in weight – they averaged about 195 grams – and would have been indistinguishable by hand, as were subsets of the ribs and axe blades. 

Standardisation is a key feature of money. However, the researchers say this can be difficult to identify in the archaeological record since ancient people had inexact forms of measurement. 

“Commodity money displays rough similarities in terms of shape and weight, because of standardisation, without necessarily following a strict metrological system,” the authors write.

“Though archaeologists have no insight in the transactions that took place, there can be no doubt that at least the rings and ribs conform to the definition of commodity money.”

More precise weighing tools appear in the archaeology record later, in the Middle Bronze Age of Europe, along with an increase in the availability of scrap bronze.