Across the island of Sardinia there are more than 7,000 ancient towers built with large blocks of local stone. Known as nuraghi, they resemble giant beehives, jutting out across the landscape. Little is known about the nuraghi or their Bronze Age architects but almost every Sardinian I met had a theory about their purpose. Some told me that they were forts; others that they were residences, places of exchange, even communication beacons. “The amazing thing is that from every single nuraghe you see another nuraghe,” Carlo Mancosu, a 34-year-old Sardinian, told me. “Now imagine a system of communication with flames or light or mirrors. I think there existed a people in a network.” ... It was this system, real or imagined, that inspired Mancosu and a group of childhood friends to found Sardinia’s first local currency: Sardex. Arts and humanities graduates with little financial experience, they built it from scratch in their home town of Serramanna as the island reeled from the financial crisis. Their hope was that the project would give them a job in the place where they had grown up. But six years later it has turned into a symbol of local action, spreading to create a new network of thousands of businesses. Together, they have traded nearly €31.3m in Sardex this year. ... For at least 150 years, business people, utopians, social reformers and eccentrics have tried to introduce local currencies, often in response to money scarcity. Their creations have taken an array of different forms, such as credit systems, time banks or paper money, and ranged from the ingenious to the absurd. Many have been shortlived — but others have outlasted the conditions that brought them into existence. ... “The permanent feature of monetary systems in Europe throughout the period from Charlemagne to Napoleon — for a good millennium — [is] a distinction between different moneys for different purposes,” says Luca Fantacci, an economist and historian at Bocconi University in Milan.