Explaining the maritime freight charges in Diocletian’s Price Edict
Walter Scheidel (Stanford University)
Princeton/Stanford Working Papers in Classics, April (2013)
In an article published in 2007, Pascal Arnaud explored the price ceilings for maritime transport stipulated in the famous tetrarchic price edict of 301 CE. In this document, maximum allowable freight charges for specific sea routes are expressed in denarii (communes) per modius kastrensis, the edict’s favored capacity unit that equaled 1.5 modii italici or about 12.9 liters. In contrast to unsuccessful earlier attempts to relate the attested prices to nautical distance, Arnaud argued that expenses reflected sailing time. Extrapolating from a handful of attested durations of sea voyages that match particular routes mentioned in the edict, he hypothesized that the number of denarii in the prices was derived from the number of days of travel, at a conversion rate of 1 denarius per day. In his view, the compilators of the text had used this schematic formula to create standardized price ceilings.
If correct, Arnaud’s intuition offers a novel way to make sense of the otherwise decontextualized freight rates reported in the edict. Earlier scholars had failed to establish a meaningful relationship between the attested prices and putative distances. In maritime transport, however, sailing time rather than distance is the critical variable. Arnaud’s approach is consequently more promising a priori grounds. Even so, he was unable to test his hypothesis in a more systematic way due to the fact no Roman sailing times are documented for most of the routes specified in the edict. This is due to the objective of the text: while Hellenistic and Roman geographical sources report normative sailing times for numerous sea routes in the Mediterranean and the Black Sea, few of them were of use to the compilators of the edict as they sought to impose price ceilings on connections between the main political centers of the Later Roman Empire, such as Nicomedia, Alexandria, Antioch, Rome and Carthage, as well as a series of coastal provincial centers, which are either named (such as Aquileia, Ephesus or Thessalonica) or have to be inferred from provincial designations (such as Tarraco or Carthago Nova for Spania or Gades for Baetica). Moreover, no fewer than four of the five cases in which Arnaud observed matches between prices in denarii given in the edict and days of travel documented elsewhere wholly or partly depend on the use of non-geographical sources that do actually not purport to provide normative information about sailing time. For these reasons, his entire reconstruction rests on extremely shaky empirical foundations.