The definition of money, in every introductory economics textbook, is a three-part function: it is a medium of exchange, a unit of account, and a store of value. What that definition does not require — a fact the textbooks glide past in a single sentence before moving on to M1 and M2 — is that money be coin, or paper, or anything else we would recognize. Across the historical record, communities have agreed to treat an astonishing variety of materials as money. The agreement is what matters. The substance is often incidental, occasionally absurd, and in at least one case so heavy that the “coins” have not moved in a century and continue to transfer ownership by verbal agreement alone.
What follows is a short catalog of currencies that genuinely functioned as currencies — not curiosities or ceremonial objects, but materials used in documented transactions to settle real debts, pay real wages, and buy real goods. The dates given are for the currency’s period of active monetary use; several persisted long after their decline as markers of prestige or tradition.
1. Rai stones of Yap (c. 1000 AD – present, ceremonial)
The most famous of unusual currencies, and the one most often cited by economists when they want to make a point about the abstraction of money. The rai are massive disks of limestone, quarried on Palau and transported by canoe across 400 kilometers of open ocean to the island of Yap, where they have served as a form of currency for roughly a thousand years. The largest rai measure up to three meters across and weigh several tons. They cannot be moved without considerable effort.
The rai are nevertheless exchanged. When a rai changes hands — in payment for a house, say, or as a marriage gift — the physical stone stays where it is. Ownership transfers by public acknowledgment alone. Everyone on the relevant part of the island knows which rai belongs to whom; the knowledge is the ledger. There is a famous rai that, according to oral tradition, was lost overboard during its transport from Palau in the nineteenth century. It sits on the ocean floor. Its ownership has continued to transfer across generations. This example is sometimes invoked to explain how bank reserves work.
2. Tea bricks (c. 900 AD – c. 1935)
Across the central Asian trade routes — from Mongolia through Siberia and into parts of Tibet — compressed tea bricks were the preferred currency for more than a thousand years. The tea was pressed into rectangular blocks weighing about a kilogram, often stamped with decorative patterns, and used to pay for goods and services. A brick was divisible: you could break off a corner for small purchases and use the remainder for larger ones.
Tea-brick currency had one substantial advantage over coin. You could drink it. In a harsh environment with unreliable water sources, a currency that doubled as a beverage and a nutritional supplement held its value in ways a copper coin did not. Tea bricks were still in use in parts of Soviet Siberia into the 1930s, and the Russian state was known to pay some of its frontier agents partly in brick tea as late as the early twentieth century.
3. Cowrie shells (c. 1200 BC – c. 1940 AD)
The shell of the small sea snail Monetaria moneta — the cowrie — may have the longest continuous monetary history of any material on this list. Cowries were used as currency in China by the second millennium BC; the Chinese character for “money,” 贝, is a stylized cowrie. Use spread across the Indian Ocean trade network, into Africa, and eventually through the Atlantic slave trade, where cowries were one of the currencies European merchants used to pay African sellers.
Cowrie currency had remarkable properties. The shells are extremely difficult to counterfeit; their natural irregularities are hard to reproduce, and artificial cowries were easily spotted by handlers. They are durable. They are light. They come pre-divided into convenient units. In parts of West Africa, cowrie money persisted into the 1940s, overlapping the early postwar period and outliving a number of European state currencies.
4. Roman salt and the salarium
Salt was an important enough trade commodity in the Roman world that one of the main roads north from Rome, the Via Salaria, was named after it. There is a persistent popular claim that Roman soldiers were paid in salt, and that the English word “salary” descends from the Latin salarium, literally “salt-money.” The second half is correct; the first half is oversimplified.
The salarium appears to have been a cash allowance given to soldiers and officials, part of which was understood to be earmarked for the purchase of salt or other provisions. Salt was not physically delivered as payment in most cases. But the term stuck, and the etymology carries a real trace of a period when salt was valuable enough to be named as a line item in a soldier’s compensation — which tells you something about the scarcity of reliable preservation methods before refrigeration.
5. Squirrel pelts in medieval Russia (c. 1000 – c. 1700)
Before Muscovy had a reliable domestic mint, one of the principal small-denomination currencies across the Russian forest zone was the squirrel pelt. Pelts were durable, standardized in size, easily assessable for quality, and available in quantity from the huge boreal forest that stretched east from the Baltic. They were used to pay taxes, to buy grain, and to settle bride-prices. The Russian word kuna, referring at various periods to a monetary unit, derives from the word for marten, reflecting the same logic applied to a more valuable pelt.
The currency had a seasonal dimension that coin did not. Pelts taken in winter were denser and worth more than pelts taken in summer. The exchange rate against grain fluctuated with the trapping season. This is, incidentally, one of the reasons silver coinage eventually displaced pelt-money: coin does not care what month of the year it is.
6. Chinese knife and spade money (c. 600 BC – c. 200 BC)
Before round coins, many of the Chinese warring states minted currency in the shape of the tools the currency was meant to replace. Cast bronze knives, about the size of a real knife, circulated as money in the state of Qi. Cast bronze miniature spades circulated in Zhou and Han. The knives had a ring at the handle so a merchant could thread several onto a cord. These were genuine currencies — stamped with mint marks, produced in graded denominations, accepted across borders — and they shed the tool-shape only gradually. The round coin with a square hole in the middle, standard across China for two millennia after 221 BC, was the descendant of the knife-money ring.
7. Colonial Virginia tobacco notes (1619 – 1775)
The Colony of Virginia had a chronic shortage of specie throughout most of the seventeenth and eighteenth centuries. Coin arrived irregularly, drained away steadily in trade with Britain, and was never sufficient for the internal economy. What Virginia had in abundance was tobacco. In 1619 the colonial legislature made tobacco formal legal tender; by the 1730s, the system had evolved into tobacco notes, which were warehouse receipts for tobacco stored in inspected public warehouses.
These notes were, effectively, a paper currency backed by a specific physical commodity held in a specific warehouse. They were used to pay taxes, salaries, and church tithes — the Anglican clergy in Virginia received their stipends in tobacco-note form, which was a perpetual source of dispute when the tobacco price moved. The system continued until the Revolution and only fully ended in the 1770s, as new continental paper currency and eventually dollar coinage displaced it.
What all this suggests
The most striking thing about these currencies is not their oddness but their stability. Several of them functioned reliably for more than a thousand years, which is longer than any modern fiat currency has existed. What they have in common is not a particular substance. It is a community agreement enforced by repeated use, combined with some physical property — difficulty of counterfeiting, durability, divisibility — that made the agreement practical to maintain. Where those conditions held, a shell or a brick or a pelt could outlast several empires. Where they failed, even gold has been devalued inside a decade.
It is sometimes said that modern money is unbacked, by which people usually mean “not backed by gold.” The currencies in this catalog suggest a different framing. Money has never really been backed by its material. It has always been backed by the willingness of enough people, for long enough, to treat it as money. The Yap stones, sitting where they have sat for centuries, transferring ownership by agreement alone, are not a primitive precursor to modern finance. They are modern finance with the intermediate layers stripped away.