I accidentally delete things all the time: an email I meant to send, a phrase I wrote but replaced, or a hard drive I thought I was fixing—only to realize I erased my computer’s operating system.

Yet, I find I can take comfort in the fact that humans have had this problem for hundreds of years. I also take comfort in the fact that even things erases can sometimes be found again. Whether on hard drives or on centuries-old parchment, what appears to be lost is often only hidden. And the technology we use—both to record information in the first place and to recover it when it’s gone—reflect the fundamental values of our time.

In the Middle Ages, monks in their libraries wrote works on parchment made from the hides of sheep and cattle. They would copy pages from the Bible, and from the works of great theologians like Augustine of Hippo. Sometimes these monks would make mistakes along the way—which, fortunately, they could easily correct by taking a knife and scraping off their ink from the sheepskin, then writing over it again. (Keep in mind that parchment is much thicker and more durable than modern paper. So a piece of parchment could be scraped several times before it would become brittle or unusable.) When they did this, the result was something called a palimpsest—a piece of parchment that has been erased and written over.

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Often, individual palimpsests are not all that interesting. But if parchment was in short supply, monks would be forced to look through their unused books and re-use parchment that was deemed less valuable. Entire books were erased and used again. In these cases, a palimpsest becomes much more exciting, a kind of mystery that begs for a detective. Ironically, when these monks erased what were, to them, unimportant words, they unwittingly launched an entire field of study, fueled by such curious detectives, hundreds of years later.

In the 19th century, an Italian priest named Angelo Mai made a career of rediscovering palimpsests from the Middle Ages and inspired many others after him. Though Mai was not the first person to discover a palimpsest, he was the first to uncover a large number of them, and the first to seriously study them in much detail.

Mai was born in Bergamo, in Northern Italy, and went to study with the Jesuits. He eventually became a professor of classical literature. When Napoleon invaded Italy, Mai was forced to return to Milan, where he first began his work on palimpsests at the Ambrosian Library in Milan. When he was able to return to Rome, he became a cardinal and a librarian in the Vatican Library. It was there that he discovered a fairly common copy of Augustine’s psalms. But what he found underneath it was remarkable: a lost work of the Roman orator Cicero from the 4th century called De Republica.

Classical scholars knew this book had once existed because it was referenced by other authors, but until 1819, when Mai found it, only small quotations survived. De Republica was perhaps Mai’s most famous discovery, and the work was especially important since Cicero was writing about the events that led to the rise of Julius Caesar, the eventual fall of the Roman Republic, and the emergence of the Roman Empire under Julius’ nephew Augustus.

Unlike today, when scholars can easily scan images into computers, then manipulate the images in multiple ways to discover what may be written underneath (without harming the original document), in Mai’s time, deciphering a palimpsest was incredibly difficult. Often, some pages were out of order; others were destroyed completely. In still other cases the parchment had been scraped multiple times making it difficult to determine what writing went with which text.

Sometimes Mai would be able to clearly see the writing underneath because the parchment had gotten dirty over time, or the parchment itself had slowly rotted away, revealing the text underneath. At other times, probably more frequently, when the text underneath was less clear, Mai used acids or other destructive methods to burn away part of the parchment and destroy the writing on top of the page; thus the work of the medieval monks who had originally erased the text, was now, paradoxically, unreadable. Despite his methods, Mai was able to recover lost works, or at least fragments of them, from many classical authors, and his work became immeasurably important in our understanding of the Greek and Roman world.

Many scholars followed Mai, and now palimpsest studies have become a popular field. Projects such as the Archimedes palimpsest project use digital imaging in order to see text written by Archimedes that was written over by Byzantine monks. The Sinai Palimpsest Project uses similar techniques to help us understand the early Christian world.

In a way that seems fittingly meta, the palimpsest as a format has taken on a new meeting from what it once was. Originally, it was just a physical document which had been erased and written over. Now, with digital media and technology, it has come to mean, particularly among media theorists, any text which has multiple layers. In other words, a web page which has multiple hyperlinks or a database which allows a user to filter results and create multiple meanings is a “palimpsest” in modern usage.

Palimpsests are now characterized by duality—the hidden/erased text and the exposed/overwritten text—and fundamentally concerned with it. By recovering what had been erased, scholars are revealing something that was meant to be deleted, thereby revealing something about the people and the societies that created these works. Palimpsests help us understand how the study of technology reflects the technology itself.

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To make a kind of loose analogy between a palimpsest and modern technology, computers often use a codec, or program that transfers information from one format into another, and a codec often loses content when moving between formats. In a way, palimpsests are a kind of codec. Palimpsests are a method that medieval programmers (monks) used to move content from one format (a copy of a book) into a blank page which they used to write a new book. Like a codec, however, information is lost when moving between formats. Once a palimpsest was scraped, though, it became difficult to recover the information that had been erased. Similarly, once a codec transfers video content from a live presentation into a video, important information may be lost and difficult to get back.

Ultimately, the technology itself—whether it is a palimpsest or a codec—reflects the value society places on certain kinds of information.

So a medieval monk, who was probably more interested in the theology of St. Augustine than in the works of Cicero, could easily eliminate what he saw as unimportant and replace it with some text that was more valuable. By the 19th century, when Mai was doing his research, there was much more interest in classical works, many of which had been lost, than in medieval works, most of which had been preserved. So, Mai saw no problem in using acid to destroy a medieval piece of parchment to recover the more important, ancient Roman, work underneath it. Fortunately, in modern times, it has become possible to recover these ancient texts without destroying what is above.

Different societies and their technologies reflect the values of their eras. And it’s easy to see how these values are realized. Palimpsests valued medieval theology over classical learning, and codecs might value easy-transfer over quality of an image. To a student of technological history, the value is in what has been lost.

In the same way that Mai tried to discover what was erased, no doubt historians of the future will do the same. So, the questions we should ask ourselves today: What information are we devaluing now? And what are the ramifications for the future? The answers will be reflected not only on the technology that we create, but on the learning we might hope to leave behind.