Archaeology

21 September 2023

From Metro Excavations: Wooden Boards from Ancient Rome. “2,000-Year-Old Oak Wood”

From Metro Excavations: Wooden Boards from Ancient Rome. “2,000-Year-Old Oak Wood”
Unearthed during the construction of Line C, they are now dated by the CNR, which has reconstructed their journey through dendrochronology: “The boards date back to 40 AD and were transported for 1,700 kilometers from the outskirts of the Empire in northeastern France.”
“An incredible feat for the time, something only the Romans could have organized,” says Mauro Bernabei, a researcher at the CNR’s Institute of Bioeconomics. “It is likely that the boards were moved southward using the currents of the Saône River, then those of the Rhône River to its mouth, about a hundred kilometers west of Marseille. From there, they were transported by sea across the Mediterranean to the Tiber River and then into the heart of Rome.”
To be precise: Via Sannio, a few hundred meters from the Basilica of St. John Lateran. Because it is here, almost 2,000 years after their long journey, that the 24 oak boards were found.
The discovery dates back to the excavation campaign carried out in Rome between 2014 and 2016, during the construction of Metro C.
“Our archaeologist colleagues found the wood preserved in an extraordinary manner,” recalls Bernabei. “Usually, this material deteriorates easily unless it is found in an extremely dry environment, or conversely, in an extremely humid one. Under Via Sannio, the water table is very high, and the boards have remained submerged in mud for all these centuries.”
But what were they used for? “As formwork into which to pour the foundations of a portico, inside a very wealthy villa, judging by the decorations found,” responds Bernabei, a dendrochronologist by profession, meaning he studies tree growth rings to obtain information about the age of the tree, the era in which it lived, and even its region of origin.

“That’s why we were involved in the study of the 24 boards found under Via Sannio,” he confirms. “From the microscopic examination of the fibers, it was immediately clear that it was oak wood. The next question was its origin.” And this is where the growth rings come into play. We are taught from childhood that their number can reveal the age of the tree. “In some boards, we counted more than 250 rings, indicating that the forest they came from was centuries-old,” explains Bernabei.

But not everyone knows that the shape of the rings reveals the era in which the tree lived (with an accuracy of one year, whereas carbon dating has an uncertainty of 100 years) and its geographical origin. “The shape of each growth ring depends on the environmental conditions in which the tree is located: a year of drought will result in a very narrow ring, completely different from the growth in a very rainy year.” And in the same geographical area, plants of the same species (in this case, oaks) will have a very similar sequence of rings because they all grew under the same conditions.

Scientists are thus able to create true dendrochronological maps that characterize different areas of the planet. “We tried to compare the growth ring sequence of the 24 boards with the database related to the Apennines, but we found no matches,” says Bernabei. “Then we tried the German database: there was some commonality, but not enough. Then we looked at the French data, and there was the surprise: the growth ring sequence matched those of oaks grown in the first century AD between the Jura Massif and the Upper Rhine Valley.”

The work of Bernabei and his colleagues, just published in the journal Plos One, is much more than a curious investigative-scientific study of the origin of some pieces of wood. It reveals that the Romans had an extraordinary logistical and transportation capacity, which they applied not only to luxury goods (from large felines used as attractions in the Colosseum to precious marbles for the emperors’ villas) but also to ordinary building materials. Including wood. “We’re not dealing with precious materials like ebony or cedar for which exceptional transport could be justified,” confirms Bernabei. “These are oak boards, 3 meters and 80 centimeters long, similar to those found in today’s DIY stores, used for foundations. ‘Ordinary’ material, in other words. Yet they had them transported from the edges of the Empire, organizing their transport for 1700 kilometers, over three rivers and a sea. It was the norm for them.”

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