Giant stone discs known as Rai stones were used as legitimate currency on the Micronesian island of Yap, with some of the coins weighing up to four metric tons.

A closer look

Giant stone discs known as Rai stones were used as legitimate currency on the Micronesian island of Yap, with some of the coins weighing up to four metric tons. Because these massive limestone circles were physically impossible to move, the local economy operated on a purely oral ledger system where ownership was simply transferred by verbal agreement, while the stone stayed exactly where it was in the jungle. In one famous instance, a stone sank to the bottom of the ocean during a severe storm, but the villagers just agreed it still had economic value and continued to actively trade its ownership rights for generations. It is fundamentally identical to how modern digital blockchain technology works, except the ancient Yapese people managed to invent a decentralized conceptual ledger system thousands of years ago without using enough electricity to completely melt the polar ice caps!