James Macksoud (Stanford University)
Portoria or customs duties are well attested throughout the Roman principate as is their operation at various levels across the empire (De Laet; Matthews; Ørsted; France; Kritzinger). This research has established that while there does not appear to have been a universal customs regime for the whole empire, there was some standardization of practices and rates, which varied internally between 1% and 5% (typically 2.5%) and externally at 12.5% or 25%. Although customs duties have a long history in the Mediterranean (Duncan-Jones 2006), the Roman Empire was the only state to have ever united the region. Additionally, the Mediterranean appears to have sustained a volume of trade under the early Roman Empire unmatched until perhaps the modern period. This high volume of trade, the Roman state’s theoretical ability to monopolize taxation within the Mediterranean, and the high rates on goods entering the empire from beyond the frontiers suggest that the potential revenue from portoria for the early imperial state may have been enormous. However, the high potential maximum revenue from portoria implicit in claims concerning the high volume of trade in this period exists in tension with estimates of the expenditures and revenues of the early imperial state which, while not ignoring the contributions of portoria to revenues, rarely afford them the massive role that might be inferred from known rates and a putatively large volume of taxable trade.
Therefore, this paper aims first to illustrate this tension between our understanding of the Roman state budget and the revenue portoria might have generated. This is done by reviewing estimates of early imperial expenditures and revenues drawn from portoria and other forms of tax and non-tax income (Duncan-Jones 1994; McLaughlin; Scheidel) and comparing these with potential maximum revenues from portoria. This involves case studies concerning the Muziris papyrus (Rathbone), the volume of imports to Rome associated with the annona (Erdkamp), and a review of shipwreck data (Parker; Wilson). The second aim is to illustrate that this tension can be resolved without the need to adjust our perceptions concerning the nominal rates of portoria, the volume of trade in the early empire, or state revenues and expenditures. This can be done by extending and adapting Scheidel’s model concerning the inefficient collection of tributum. In essence, this involves accounting for various forms of wastage via tax exemptions, tax evasion, and the rent-seeking behavior of state agents responsible for collecting portoria, including both local magistrates and publicani (Brunt). These factors effectively lowered both the quantity of taxable trade and increased extraction costs, thereby leading to substantially lower net-revenues for the Roman state. These three factors are illustrated with case studies concerning the lex portorii Asiae (Cottier et al.), pseudo-Quintilian Declamation 359, and the lex portorii provinciae Lyciae (Takmer). By connecting scholarship on Roman trade to that on state dynamics, this paper illustrates that arguments for the economic complexity of the early Roman empire need not be incompatible with a minimalist view of Roman state institutions and their capacity.