When ancient oak planks were unearthed during subway construction in Rome, Mauro Bernabei and his team examined the growth rings in the wood to determine where these planks came from. By comparing the growth rings on the planks to records of similar rings in oaks from Europe, the team could trace the wood to the Jura region of France, hundreds of kilometers from Rome. Because timber could only have been transported from distant Jura to Rome by boat, the team’s findings suggest the complexity of Roman trade routes.