The late-antiquity environmental crisis in Emilia region (Po river plain, Northern Italy): Geoarchaeological evidence and paleoclimatic considerations

Abstract

For about four decades in Italy local, scientific literature has occasionally dealt with fluvial avulsions, suggesting they should be considered as genetically linked to a peculiar climatic worsening that occurred in the late-6th century AD (the so-called “Paul the Deacon Deluge”). Research performed by the Soprintendenza per i Beni Archeologici dell'Emilia-Romagna over the last few years has allowed better definition of the timing of a more articulated alluvial history, mainly concerning the Roman Imperial age and Late-Antiquity (1st–6th century AD). The main stratigraphic details of fourteen selected archaeological excavation sites (eleven recently surveyed and three reviewed from the literature) performed in the cities of Modena, Bologna and related surroundings have been summarized. Eleven 14C dates, ranging between the years 130 AD and 810 AD, allowed us to chronologically delimit a first framework for the riverbed network behaviour during ancient times in the central part of the region. The alluvial process appeared to be continuous throughout the time span examined. The fan trench was the most sensitive reach of the river system. It started to aggrade during the 4th century AD. During the 5th century AD and probably after the end of the 6th century AD, a number of avulsions occurred. This indicates that the fluvial system was in a metastable equilibrium, whose behavioural threshold was finally overcome. Hence, the importance of the supposed year 589 AD crisis (the “Deluge”) appears to be less than previously supposed. The riverbed aggradation became evident immediately after the Roman Empire's economic and demographic crisis of the 3rd century AD, and it was probably due to the loss of the land preservation systems in the mountain catchment areas. The long duration of the aggradation phase suggests that more than one human settlement phase in the minor catchment areas and/or a minor climatic worsening pulse probably occurred during the 5th century AD. The starting of the aggradation also coincided with the end of the Petit Maclu 1 high level phase of the European lakes. Notwithstanding this, the climate's role as a forcing co-factor can still be hard to evaluate positively due to the lack of local proxy data.