But by July, when a coalition of new leaders consolidated control and began tearing down some of the city’s most important burial shrines, the heads of Timbuktu’s libraries had already been working quietly for months to move and hide their collections—one of the most significant troves of unique med­ieval manuscripts in the world. And among the first materials that they smuggled out were something surprising: hard drives.

These hard drives were packed with digital backups of thousands of precious library documents. Though today Timbuktu is a remote and dusty city of 54,000 at the edge of the Sahara, 500 years ago it was a major commercial crossroads and a great center for scholarship. Copied onto those disks were scanned versions of some of the world’s most important surviving medieval manuscripts, texts on Islam, politics, math, and science that illuminate the city’s past as a center of learning.

In the last decade, Timbuktu’s libraries have been working with partners in the United States, South Africa, and France to create digital archives of its crumbling documents. Expensive scanners and digital cameras have been ferried up the slow Niger River or along the long road to the isolated city to capture these texts electronically and in some cases to post them online, making them widely available to scholars for the first time.

In the broad recent push to digitize libraries around the world, most of the rationale has been about such access. The team behind the Digital Public Library of America project, for example, which includes Harvard University and the Library of Congress, says its goal is to “make the cultural and scientific heritage of humanity available, free of charge, to all.” A similar project at Google Books aims to digitize all the world’s estimated 130 million books by 2020. But when Timbuktu became the target of jihadist rebels, the urgent efforts to document and save its manuscripts made it an important test case for a different role for digitization entirely: to make backup copies of unique, endangered collections that otherwise might be lost to us completely.

Turning to digital copies as a tool for cultural preservation carries risks, and raises its own questions: What do you prioritize? How do you handle the expense and potential damage to priceless old documents? What about the fact that these digital files, too, are unstable?

But what happened in Mali this year suggests exactly how high the stakes can be. Last month, as the rebels retreated from the city, they stormed into one of the city’s largest libraries, the state-sponsored Ahmed Baba Institute, and burned everything they could find. For a few days, before the institute and other libraries revealed just how many original manuscripts they had hidden away, it seemed possible that whatever digital copies had been spirited out or placed online would be the only versions we had left.

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In its heyday in the 15th and 16th centuries, when trade in salt and gold was thriving and its great mosque made it a religious center, Timbuktu was populated by scholars from across the Muslim world, who collected and wrote books on the classical texts of Islam and on contemporary questions of medicine, astronomy, math, politics, and more. After a Moroccan force invaded in 1591, the city’s intellectual life faded. But the manuscripts survived, handed down through families for centuries and hidden whenever the political situation turned dark.

Over the past four decades, those documents have begun to be consolidated into bigger collections that have attracted the attention of the outside world. Since 2000, Timbuktu’s libraries have received funding from groups including the government of South Africa—whose then-president, Thabo Mbeki, called the documents “the most important cultural treasures in Africa”—and from Western institutions such as the Ford Foundation. Often, this outside funding for conservation included provisions for making digital copies.