The paper shows the analytictal results obtained from the archaeometric study carried out on a Roman sarcophagus, known today as the tomb of King Ramiro II of Aragon, called “the Monk”. Non-destructive spectrophotometric colour testing, petrography, cathodoluminiscence (CL microfacies and quantitative CL) and C-O isotopic techniques were applied in order to investigate its marble provenance. The characterization is based on available data of the most important ancient quarries around the Mediterranean Sea and the nearest French Pyrenean districts. The results prove the use of Proconnesian marble from Marmara Island in Turkey.