June 10, 2010

Aqua Traiana

Back in January, a couple of British documentarians found the source of the Aqua Traiana, the 2nd century AD aqueduct that started about 35 miles north of Rome near Lake Bracciano. From my very limited knowledge of aqueducts, it seems like little is known about the Traiana, at least in terms of the volume of water that was imported to Rome each day and possibly in terms of its water depots (castella) in Rome, although it appears to have supplied the Janiculum with water. Because Frontinus, the water commissioner of Rome in the 1st century AD, doesn't have volume figures for the Traiana (as he predated its inauguration), I couldn't use it in my construction of a strontium isotope model for the ancient city.

Bracciano, however, is a volcanically formed lake, and the strontium isotope ratios of volcanic geology increase the further north one goes in the Italian peninsula. It is therefore possible that people living in Rome in the 2nd century and later could obtain a strontium value as high as perhaps .7107, which is the only published ratio for Bracciano I could find. And since it's volcanic, it is likely that the water has a high strontium content too, which means it would dominate the signature of someone who drank a mixture of water from Bracciano, the local Colli Albani (.7090-.7103), and the eastern aqueduct sources in the Monti Simbruini (.7079-.7080).

There are estimates of the volume of water the Traiana brought into Rome (e.g., 1,300 litres per second, or roughly 30 million gallons of water per day). If this figure is right, it has the possibility to substantially alter the percentage of high-strontium water available in the city, as it's about the same amount as Romans were importing from aqueduct sources in the local Colli Albani and half the amount they were importing from the low-strontium Monti Simbruini sources. As a way forward in modelling the strontium range of ancient Rome in order to investigate immigration, it is important to measure the strontium isotope ratio and concentration of the water from the source of the Traiana, which is why I've been watching the issues around the spring (and its associated architecture) unfold.

In spite of all the initial excitement about the aqueduct source and all the architecture and hydrological equipment, the owner of the land on which the aqueduct was found is suddenly not too keen on having archaeologists swarm his property to excavate this incredibly important feature in Roman hydrology. Apparently, he wants to do it himself to reap the rewards of finding priceless antiques. I hope that Italian authorities are successful in getting a permit to excavate or an injunction or whatever they need to preserve the site for professional inspection. And I hope that one day I (or some other enterprising geo- or archaeologist) can sample the water to get strontium isotope ratios and concentrations that would be useful to both bioarchaeologists and geologists in the area.

Still, based on my strontium isotope ratios from human remains, there are very few individuals over .7100, well within the expected range for people drinking water from the Colli Albani. A few individuals did have slightly higher ratios, though, such as .7104 - which could mean they came to Rome from a few dozen miles north, or that they drank water in Rome from the source waters of the Aqua Traiana. The strontium isotope analysis of Imperial Romans was far more complex than I initially thought it would be. Fortunately, between two-end-member models and the addition of oxygen isotope analysis, the complications of the aqueducts can be somewhat obviated. Of course, as with all research, analysis of additional samples (of people, animals, and water sources) would generate substantial progress in looking at migration to Rome through chemical means.


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