Ancient Rome represents a rare opportunity to compare a longitudinal study of rainfall records with an unusually extensive historical record covering more than a millennium. However, the few existing climate records covering this period and region suffer from dating uncertainty, discontinuity and human impact. This paper investigates the potential of dark layering in calcium carbonate deposits formed in past water systems as a well-dated and high-resolution proxy for rainfall distributions, through a case study on ancient Rome’s Anio Novus aqueduct. Such a proxy would have broad applicability, since carbonate deposits are found in water systems from Australia’s Great Artesian Basin to pre-Columbian North America. Dark-coloured layers within deposits from this aqueduct have multi-scalar distribution and elevated organic concentrations that are consistent with formation during the organic-rich flows of the Anio Novus’s source water during storms (Keenan-Jones et al. 2014). This paper will present stable isotope ratio measurements from the Anio Novus deposits in order to investigate the time period over which these dark layers formed. Apart from its palaeoclimatic value, this rainfall record will illuminate the influence of climate on flooding, disease and fire, all of which were serious concerns in densely-populated ancient Rome.


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