The Empire Strikes Coins: Islamic Conquests, Iconoclasm and Currency Debasement in Byzantium, 650-900 Ad

Abstract: The long and difficult history of the Byzantine, or, more precisely, East Roman, Empire provides a plethora of contexts for research into the institutions and political economy of medieval states. In the present paper we concentrate on monetary developments in Byzantium between 650 and 900 AD. This period saw three important and interdependent developments: An economic and fiscal crisis due to the Islamic conquests, important administrative and military reforms, and ecclesiastical strife. Our main aim is to throw a light on the possible relationships between the debasement of the Byzantine gold currency (the solidus) and politico-economic developments. More specifically, we aim at elaborating an empirical picture of how the purities of gold coins issued by the imperial mints of Sicily and Constantinople were affected by various politico-economic variables. In doing so, we exploit the recent advances in the field of numismatics regarding the analysis of Byzantine coinage, treating coins as data sources which can provide a lot of information about the relevant politico-economic background. For our empirical approach we have created a dataset with time series data over 250 years regarding the purity of gold solidi struck in Sicily and Constantinople, the estimated size of Byzantine imperial territory, violent regime change, civil wars, dynastic transitions etc.; although the results are still preliminary there appears to be a significant influence of territorial losses and coups d'etat. This result may provide confirmatory evidence of a mainly fiscal motivation to debase the gold currency.