Oaks Hold the Keys to Understanding Ancient Rome

Oaks have been used to trace trade routes in the Roman Empire in the 1st century CE. Excavations for a subway line in Rome unearthed the remains of a portico made of oak planks. Using dendrochronological analysis, researchers were able to determine not only the age of the wood but their provenance. Oak-tree rings record weather patterns: the amount of rain that falls during a growing season determines the width of a growth ring, so the pattern of an oak plank’s rings can be matched to the climate of a particular region, based on reference chronologies that have been established on the basis of other remains. In a paper recently published on PLoS One, Mauro Bernabei of Italy’s National Research Council and his colleagues report that they were able to determine that oak planks from the foundations of a patrician villa in Rome are from up to 300-year-old oak trees, felled between 40 and 60 CE in north-eastern France, possibly in near-natural woodlands of the Jura Mountains. They also deduce how the timber reached Rome using still-existing waterways: it was rafted and floated down the principal rivers of the province of Gaul, the Saône and Rhône, and then sailed across the Mediterranean Sea to be finally taken up the river Tiber to Rome. This is the first proof that oak trees grown in Roman provinces north of the Alps were used for the construction of buildings in ancient Rome.

But it is not the first time that oak-tree rings have been used to study the Roman Empire. In a paper published in 2018 in Economic Letters, Cornelius Christian of Brock University and Liam Elbourne of St Francis Xavier University identify a strong association between rainfall patterns and the duration in power of Roman emperors. They analyzed precipitation data taken from rainfall-sensitive oak-tree rings across the Roman frontier and eastern Germany, and combine it with data on assassination of emperors (about one in five were assassinated). They found that a decline in annual rainfall significantly increased the probability that an emperor would be assassinated the following year. One wonders how Roman emperors would have behaved at a Climate Change Conference . . .

Further reading

Bernabei, M., Bontadi, J., Rea, R., Büntgen, U., Tegel, W. 2019. Dendrochronological evidence for long-distance timber trading in the Roman Empire. PLoS ONE 14(12): e0224077. https://doi.org/10.1371/journal.pone.0224077

Christian, C. and Elbourne, L. 2018. Shocks to military support and subsequent assassinations in Ancient Rome. Economics Letters, Elsevier, vol. 171(C), pages 79-82. https://doi.org/10.1016/j.econlet.2018.06.030