Revealing Letters in Rolled Herculaneum Papyri by X-Ray Phase-Contrast Imaging

ARTICLE Received 17 May 2014 | Accepted 19 Nov 2014 | Published 20 Jan 2015 DOI: 10.1038/ncomms6895 Revealing letters in rolled Herculaneum papyri by X-ray phase-contrast imaging Vito Mocella1,*, Emmanuel Brun2,3,*, Claudio Ferrero2 & Daniel Delattre4 Hundreds of papyrus rolls, buried by the eruption of Mount Vesuvius in 79 AD and belonging to the only library passed on from Antiquity, were discovered 260 years ago at Herculaneum. These carbonized papyri are extremely fragile and are inevitably damaged or destroyed in the process of trying to open them to read their contents. In recent years, new imaging techniques have been developed to read the texts without unwrapping the rolls. Until now, specialists have been unable to view the carbon-based ink of these papyri, even when they could penetrate the different layers of their spiral structure. Here for the first time, we show that X-ray phase-contrast tomography can reveal various letters hidden inside the precious papyri without unrolling them. This attempt opens up new opportunities to read many Herculaneum papyri, which are still rolled up, thus enhancing our knowledge of ancient Greek literature and philosophy. 1 CNR-IMM-Istituto per la Microelettronica e Microsistemi-Unita` di Napoli, via P. Castellino 111, 80131 Napoli, Italy. 2 ESRF—The European Synchrotron, 71 Avenue des Martyrs, CS40220, F-38043 Grenoble Cedex 9, France. 3 Ludwig-Maximilian-Universita¨t, Am Coulombwall 6, 85748 Garching bei Mu¨nchen, Germany. 4 CNRS-IRHT-Institut de Recherche et d’Histoire des Textes, 10 rue Molitor, 75016 Paris, France. * These authors contributed equally to this work. Correspondence and requests for materials should be addressed to V.M. (email: [email protected]). NATURE COMMUNICATIONS | 6:5895 | DOI: 10.1038/ncomms6895 | www.nature.com/naturecommunications 1 & 2015 Macmillan Publishers Limited. All rights reserved. ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms6895 he explosion of Vesuvius in 79 AD, the most famous science, palaeontology and archaeology, as well as several eruption of this volcano1, destroyed several Roman towns industrial areas, the image contrast mechanism is based on Tin Campania, especially Pompeii and Herculaneum. The differential X-ray absorption within a compound object. This eruption buried these sites under very thick layers of volcanic technique works particularly well for discriminating strongly material, preserving them in what became an exceptional absorbing materials, such as bone, from weakly absorbing opportunity for students of ancient Greco-Roman culture. After materials such as soft tissues18. However, many important initial, sporadic discoveries by well-diggers and treasure hunters, applications in biology, medicine and even materials science Charles, the Bourbon King of Naples, ordered that they be require the detection of absorption variations between weakly explored in what became the first systematic archaeological absorbing (low-Z) materials, like the ink of the Herculaneum excavations2–5. scrolls and its papyrus support. As the variations in this case are After a first discovery of papyrus rolls in 1752 (ref. 6), in 1754 minimal, XCT does not appear to be a suitable technique, but one (refs 5,7,8), from late February through August, an entire library promising approach that has proven to overcome these was discovered in a small room of a huge villa (thought by some limitations is the X-ray phase-contrast tomography (XPCT) to have belonged to the wealthy Roman statesman Calpurnius technique19. Unlike XCT, XPCT exploits variations in the Piso Caesoninus9) containing hundreds of handwritten refractive index (that is, X-ray phase shifts) between structures carbonized papyrus scrolls carefully stored in shelves covering that absorb quite uniformly within a composite object, thus its walls. This rich book collection, consisting principally of significantly enhancing the image-contrast effect. More precisely, Epicurean philosophical texts, is a unique cultural treasure, as it is in propagation-based phase-contrast imaging (PBI), quasi- the only ancient library to survive together with its books. The coherent radiation illuminates the object producing a spatially texts preserved in these papyri, now mainly stored in the Officina variant phase shift of the X-ray beam20,21. As the X-rays dei Papiri in the National Library of Naples10, had been unknown propagate from the sample, portions of the wavefront that have to scholars before the discovery of the Herculaneum library, since experienced different deflections in the sample generate they had not been copied and recopied in late Antiquity, the characteristic patterns. Due to Fresnel diffraction, the phase middle ages and Renaissance. shifts are transformed into measurable intensity variations, which A quite sophisticated mechanical method for unrolling the best are recorded by a detector located at an appropriately chosen preserved scrolls—applicable to their final, interior parts that are distance. Over the last 15 years, phase-contrast imaging has less than a third of their original length—dreamed up in 1754 by undergone rapid progress, and various methods aimed at Antonio Piaggio2–5 continued to be used until the beginning of obtaining the phase information have been developed. In the the 20th century on those scrolls that could in principle withstand literature, several articles22–27 show the suitability of this the physical stress imposed by the process. Different opening technique for discriminating different materials of similar techniques, all less effective, have been tried over the years11 until composition within a single object, as in the case of black the so-called ‘Oslo method’ was applied in the 1980s on two charcoal ink and carbonized papyrus. Herculaneum scrolls now in Paris12 with problematic results, Here we examine two of the six Herculaneum scrolls (one since the method required the rolls to be picked apart into small unrolled and the other still rolled-up) presented as a ‘gift’ to the pieces13. All further attempts to unroll the papyri or to separate Premier Consul Napoleón Bonaparte in 1802 and currently their layers mechanically had been abandoned until now to belonging to the collection of the Institut de France. The first preserve their physical integrity and the possibility of reading sample is a fragment of the unrolled scroll, PHerc.Paris. 1, while them as continuous texts one day, because an excessive the second (PHerc.Paris. 4) is an (almost) entire rolled-up scroll. percentage of these ancient texts was irretrievably lost by the Our results show that XPCT is the first non-destructive technique application of such methods. that enables us to read many Greek letters and some words in the On the other hand, in the last 20 years a great deal of progress interiors of rolled-up Herculaneum papyri without impairing has been made in reading the Herculaneum texts that had already their physical integrity, as the previous unrolling techniques had been unrolled. In particular, the use of binocular microscopes, done. This is extremely important because the fragility of and digital photography, employing ‘multispectral’ filters that carbonized papyri requires the most careful manipulation. isolate a narrow portion of the near-infrared spectrum, have both improved the readability of these texts considerably14,15. Unfortunately, these techniques are not applicable to texts that Results remain rolled-up due to the superposition of papyrus layers and Sample characteristics. The Herculaneum scrolls were burnt by a the weak penetration of most types of radiation exploited by blast of furnace-like (c. 320 °C) gas from the volcano into a vastly multispectral techniques. homogenous sample matrix. In Antiquity, the most common In Antiquity, papyri were written using a black carbon-based ink writing material used for books and other documents was obtained from smoke residues, the density of which is almost the papyrus. The stalks of papyrus plants were cut into thin strips, same as that of the carbonized papyrus. Until now, therefore, it has then two strips were laid atop and perpendicular to one another; appeared impossible to distinguish ink from papyrus inside a these strips were then combined by pressing them until the papyrus roll using the penetrating radiation of a conventional X-ray plant’s natural starch that acted as a paste. The resulting sheets of source and technique, where the X-ray image contrast is based papyrus were then smoothed and bleached. A papyrus roll con- exclusively on the X-ray-absorption patterns of different materi- sisted of some number of such sheets pasted together end on end. als16. The X-ray fluorescence imaging method has been successfully The resulting sheet, which could reach 15 m or more in length, applied to the chemical mapping of writings in ancient manuscripts was then rolled up from right to left, so that it could be read from and palimpsests that are covered by other writings, paintings or left to right. Papyrus writing material, therefore, consisted of two mold, for example17. However, to read the writing on surfaces layers, whose fibres ran perpendicular to one another; the scribe hidden within papyrus scrolls or on layers of fragmentary rolls would usually write the text in vertical columns on the side of the below their exposed upper surfaces, a different technique is papyrus sheet where the horizontal fibres were uppermost. The needed—one that discriminates modifications inside the scrolls. carbon-based ink he used did not penetrate into

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