Belgian Marble and a Trip to the Vatican

Written by Dr Judith Bunbury, Department of Earth Sciences, University of Cambridge

This black marble was part of an adventure that took me into geo-history, up a painter’s scaffold in the Vatican, and on a tour of monastic quarries in Belgium.

The trail began in 2003 with an invitation to coffee with Professor Jo Story of Leicester University. She showed me a blurry photocopy of an inscription in the Vatican that was 10 metres off the ground and said to be made of basalt, a hard volcanic rock. The image was of a large black stone slab, with a poem, commissioned by Charlemagne as an epitaph for Pope Hadrian in 799 AD. The letters were beautifully cut, and it seemed improbable that such a large smooth slab was actually basalt, but the authors of the paper, who had examined it from ground level, were certain that it was.

We prepared for a trip to Rome, and a scaffold was already booked to examine the slab when Pope John Paul II’s health took a turn for the worse and the Vatican cancelled our booking, in case they had to organise a funeral. When he fortunately recovered, the scaffold was re-booked and we promptly headed to Rome.

One of my foibles is that I am scared of heights, but I managed to wobble my way up the scaffold to see the slab. On arriving, the first things I saw were coral fossils. We were prepared for basalt, but I had done no preliminary research on black marbles. Jo and I made a rubbing in black crayon of the whole slab, from the top two storeys of the scaffold and then I carefully recorded the fossils and photographed them. Joining us perched above the tourists in St Peter’s Rome were a team from La Sapienza University who kindly brought their portable XRF (X-ray fluorescence) machine to analyse the stone.

Back in Cambridge, I pored over samples in the Watson collection. It was here that I identified the black Belgian marbles from St Anne as the best match (number 155 and 156 in the Watson decorative stones and marble collection). Examining them in detail and combing fossil books and field guides from the library while Jo interrogated museum catalogues for black marble, we narrowed the search to an area near Aachen. Then we headed to Belgium where Professor Eric Groessens of the Belgian Geological Survey took us on a tour of churches, quarries, museums, paving stones and street furniture, looking for the match for our epitaph. Fortunately, the area has abundant monasteries that brew beer, make cheese and bread and sell them to passers-by, so we were well refreshed.

Returning to Cambridge we made thin sections of our candidate marbles, conducted more XRF and compared them to the observations made in Rome. The jury was still out, and we reported back to the conservators at St Peter’s that we could not be completely certain without thin section evidence, which was unfortunately not available. By return a jiffy bag with a Vatican mail stamp arrived with a small chip from the inscription. I was appalled but we were committed now and, finally, narrowed it down to the Sclayn Quarry, around 5km east of Namur, an area of land originally owned by Plectrude, Charlemagne’s mother.

Taken in conjunction with Jo’s historical research, we conclude that Charlemagne commissioned the epitaph from the finest poet of his age, Alcuin of York, and had it carved by the finest hands in Aachen in stone from his mother’s homelands. ‘Carolus Rex’ (King Charlemagne) appears at eye-level (in the original placement) while the Pope whom it commemorated was marginalised to the top and bottom of the slab. The whole was commissioned in black marble with gold lettering, to resemble a Roman legal text, and shipped to Rome as a manifesto for the brilliance of Charlemagne. Within a year of presenting it, he was crowned Holy Roman Emperor.