Using cutting-edge technology, researchers from the University of Oxford and the Netherlands have uncovered a Mexican codex which has been hidden beneath a layer of plaster and chalk since the 16th century. The codex was concealed on the back of a later manuscript known as the Codex Selden, which dates from around 1560, kept in the Bodleian Library.Codex Seden is one of less than 20 manuscripts made before the European conquest of the Americas still in existence. These scripts use codes of pictures and symbols in bright colors to recount the history of ancient cities, wars and genealogies of dynasties. According to Oxford University, this is the first time an early Mexican codex has been proven to be a palimpsest, or an older document which has been covered up and reused, obscuring the original.Ludo Snijders from Leiden University, who conducted the research with David Howell from the Bodleian Libraries said, “After four or five years of trying different techniques, we’ve been able to reveal an abundance of images without damaging this extremely vulnerable item. We can confirm that Codex Selden is indeed a palimpsest”.“What’s interesting is that the text we’ve found doesn’t match that of other early Mixtec manuscripts. The genealogy we see appears to be unique, which means it may prove invaluable for the interpretation of archaeological remains from southern Mexico.”Although archeology scholars had long expected Codex Selden is a palimpsest, until very recently no technique has managed to unveil the covered manuscript in a non-invasive way. The manuscript underwent invasive tests in the 1950s when a back page was scraped back, uncovering clues that an earlier codex could lie beneath. However, ancient Mexican scrolls used organic paints to create the vibrant manuscript images, and these paints do not absorb x-rays, which meant the widely used x-ray analysis was ineffective on this artefact.This time, scientists used ‘hyperspectral imaging’ to reveal the pictures that lay beneath, publishing their findings in the Journal of Archaeological Sciences. The hyperspectral imaging scanner was acquired two years ago when the Bodleian Libraries and Classics Faculty made a bid to the University’s Fell Fund.Oxford classicist Dr Charles Crowther says use of the new scanner will benefit numerous humanities departments across Oxford University, allowing them to analyse previously inaccessible artifacts. He said, “Hyperspectral Imaging (HsI) is certainly the most exciting development in this field in that time. Its application to manuscripts in Oxford collections, whether carbonised Herculaneum papyri, parchment Achaemenid letters, or erased marginalia in the First Folio, has the potential to resolve details that previously have been unattainable and to bring to light significant new texts.”The Bodlian Library is in possession of four other pre-colonial Mesoamerican codices: Codex Laud, Codex Bodley, Codex Mendoza and the Selden Roll, named after their former European owners.