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The shape of the Roman world: modelling imperial connectivity

  • Walter Scheidel (a1)
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1 The best conventional map resource is, of course, Talbert, R. J. A. (ed.), Barrington atlas of the Greek and Roman world (Princeton, NJ 2000) (now also available as a tablet app); the best study of the Peutinger Map is his Rome's world: The Peutinger Map reconsidered (Cambridge 2010), with the splendid online resources at For ancient maps in general, see now the references in Talbert's ‘Maps’, Oxford Bibliographies, June 26, 2012, DOI: 10.1093/OBO/97801953896610075.

2 Braudel, F., La Méditerranée et le monde méditerranéen à l'époque de Philippe II (Paris 1966) 326 (poorly rendered as the ‘first enemy’ rather than “enemy number one”, in the English translation of 1972).

3 Ibid. 331-39, drawing upon Sardella, P., Nouvelles et spéculations à Venise au début du XVIe siècle (Paris 1948).

4 W. Scheidel and E. Meeks, “ORBIS: The Stanford Geospatial Network Model of the Roman World”, Version 1.0 launched May 2, 2012, at For other collaborators, see the ‘Credits’ page on that site.

5 See the preliminary exposition by S. Arcenas, “ORBIS and the sea: a model for maritime transportation under the Roman empire”, ORBIS/Applying ORBIS, at

6 The relevant sections are ORBIS/Understanding ORBIS/Introduction, and ORBIS/Building ORBIS/Historical evidence and …/Geospatial technology, at (with full bibliography). The technical details will be dealt with more extensively in a forthcoming publication on travel speed in the Roman world.

7 For more detail, see ORBIS/Understanding ORBIS, at

8 Total allowable charges per modius kastrensis are 698 denarii communes for 55 sea-routes specified in the Prices Edict for which ORBIS computes a total length of 104,403 km in the month of July. This yields a mean of 0.00067 denarii per kg of wheat per km. River travel is priced at 1 denarius per modius (?kastrensis) for 20 miles downriver, and 2 denarii upriver, or 0.0034 and 0.0068 denarii per kg of wheat and km. (The cost of provisions for the crew, which were also included, can be estimated to have been comparatively trivial.) Land transport by wagon is priced at 20 denarii for 1,200 Roman pounds per Roman mile, or 0.035 denarii per kg of wheat per km. Earlier calculations sometimes lacked access to more recently discovered information regarding river transport, and were generally unable to establish average maritime charges per km, relying instead on supposedly representative routes: e.g., Duncan-Jones, R., The economy of the Roman Empire (2nd edn., Cambridge 1982) 368; Hopkins, K., “Models, ships and staples,” in Garnsey, P. and Whittaker, C. R. (edd.), Trade and famine in classical antiquity (Cambridge 1983) 104; DeLaine, J., The Baths of Caracalla (JRA Suppl. 25, 1997) 210–11.

9 Duncan-Jones ibid. 368; Dubois, H., “Techniques et coûts des transports terrestres en France aux XIVe et XVe siècles,” in Marx, A. V. (ed.), Trasporti e sviluppo economico, secoli XIII-XVIII (Florence 1986) 290; Masschaele, J., “Transport costs in medieval England,” Econ. Hist. Rev. 46 (1993) 277; P. Bol, “Transportation costs in the Song: ChinaX Project Report 2012,” with references (I am indebted to the author for sharing this unpublished survey with me). Significantly lower ratios attested for Tang China and inferred for mediaeval England (Masschaele, ibid.; Bol, ibid.) are hard to explain.

10 For positive assessments of (earlier) ratios, cf. Hopkins (supra n.8) 104; Laurence, R., The roads of Roman Italy (London 1999) 99.

11 Scheidel, W., “Explaining the maritime freight charges in Diocletian's Prices Edict,” JRA 26 (2013) 464–68.

12 Contra, e.g., Hopkins (supra n.8) 103-4, and especially Arnaud, P., “Diocletian's Prices Edict: the prices of seaborne transport and the average duration of maritime travel,” JRA 20 (2007) 334.

13 See Johnson, A. C., Roman Egypt to the reign of Diocletian (Baltimore, MD 1936) 400–24.

14 It is unclear whether this high ratio can be blamed on Roman-era harnessing, which used to be considered inadequate but has now found defenders: see Polfer, M., “Der Transport über den Landweg – ein Hemmschuh für die Wirtschaft der römischen Kaiserzeit?,” Helinium 31 (1991) 275, and especially Raepsaet, G., Attelages et techniques de transport dans le monde gréco-romain (Brussels 2002).

15 Scheidel, W., “A comparative perspective on the determinants of the scale and productivity of maritime trade in the Roman Mediterranean,” in Harris, W. V. and Iara, K. (edd.), Maritime technology in the ancient economy (JRA Suppl. 85, 2011) 2137, with discussion of mediaeval and early modern comparanda.

16 For Britain, see Carreras, C., Una reconstrucción del comercio en cerámicas: la red de transportes en Britannia (Barcelona 1994); La economía de la Britannia romana: la importación de alimentos (Barcelona 2000). The most detailed study, for part of the Iberian peninsula, is Soto, P. de, Anàlisi de la xarxa de comunicacions i del transport a la Catalunya romana: estudis de distribució i mobilitat (Ph.D. diss., Universitat Autonoma de Barcelona 2010). See also id. and Carreras, , “La movilidad en época romana en Hispania: aplicaciones de redes de análisis (SIG) para el estudio diacrònico de las infraestructuras de transporte,” Habis 40 (2009) 303–24; Soto, P. de, “Transportation costs in NW Hispania,” in Carreras, C. and Morais, R. (edd.), The Western Roman Atlantic façade: a study of the economy and trade in the Mar Exterior from the Republic to the Principate (BAR S2162; Oxford 2010) 3143; Carreras, C. and Soto, P. de, “The Roman transport network: a precedent for the integration of the European mobility,” Historical Methods 43 (2013) 117–33. For the entire empire, see now C. Carreras, “An archaeological perspective,” in id. and Morais ibid. 7-19.

17 Leidwanger, J., Maritime archaeology as economic history: long-term trends of Roman commerce in the northeast Mediterranean (Ph.D. diss., Univ. of Pennsylvania 2011) 90121.

18 The classic exposition is that by Chase-Dunn, C. and Hall, T. D., Rise and demise: comparing world-systems (Boulder, CO 1997) especially 5255.

19 Aside from classic sea-routes for military transfers, such as from Sicily to Africa or across the Strait of Otranto, most references are to the maritime movement of supplies, not of the troops themselves: e.g., Roth, J. P., The logistics of the Roman army at war, 264 BC-AD 235 (Leiden 1999) 189–95; cf. also Starr, C. G., The Roman imperial navy, 31 B.C.-A.D. 324 (Ithaca, NY 1941) 167208; Reddé, M., Mare nostrum (Paris 1986) 370–99. Except for the above-mentioned routes, explicit references to longer-range maritime troop-transfers for campaigns under the monarchy are extremely rare: Starr ibid. 186-87 and 192; Reddé ibid. 373 (who, however, tries to infer a larger number of such operations indirectly from epigraphic records such as dedications by naval personnel).

20 Roman sea-routes in the Atlantic are generally poorly known: for recent scholarship, see Carreras and Morais (supra n.16). For sea-ports on rivers in Britain, cf. Rippon, S., “Coastal trade in Roman Britain: the investigation of Crandon Bridge, Somerset, a Romano-British transshipment port beside the Severn estuary,” Britannia 39 (2008) especially 8589.

21 For this episode, see Zos. 2.10.2-3 (3,000 soldiers reached Sirmium from Raetia in 11 days, followed by 20,000 troops on foot), with Himmler, F., Konen, H. and Löffl, J., Exploratio Danubiae: ein rekonstruiertes spätantikes Flusskriegsschiff auf den Spuren Kaiser Julian Apostatas (Berlin 2009). Other instances are limited to the German campaign of A.D. 16 (Tac., Ann. 2.5) and a few campaigns along the Euphrates: Reddé (supra n.19) 357-58 and 362. The most detailed study of Roman riverine military assets is Konen, H. C., Classis Germanica: die römische Rheinflotte im 1.-3. Jahrhundert n.Chr. (St. Katharinen 2000). More generally, see now Campbell, B., Rivers and the power of ancient Rome (Chapel Hill, NC 2012) 160–99.

22 For discussion, see most recently Kolb, A., Transport und Nachrichtentransfer im Römischen Reich (Berlin 2000) 310–11. Vegetius (1.9) prescribes a training march for recruits of 20 miles in full gear that was to be completed within 5 summer hours, which may reflect contemporary expectations of what constituted a reasonable daily effort. Cf. also Vigneron, P., Le cheval dans l'antiquité gréco-romaine (Paris 1968) 158; Silverstein, A. J., Postal systems in the pre-modern Islamic world (Cambridge 2007) 1213. This speed could be matched by moderately loaded mules: Cotterell, B. and Kamminga, J., Mechanics of pre-Industrial technology (Cambridge 1990) 194. 20 km per day is certainly feasible as a longer-term average (Kolb ibid. 311) and also works for heavily loaded mules (Cotterell and Kamminga ibid. 194). Cf. also Engels, D. W., Alexander the Great and the logistics of the Macedonian army (Berkeley, CA 1978) 16 (15 km per day for Alexander the Great); Ludwig, F., Untersuchungen über die Reise- und Marschgeschwindigkeit im XII. und XIII. Jahrhundert (Ludwig 1897) 182–83, and McCormick, M., Origins of the European economy: communications and commerce, A.D. 300-900 (Cambridge 2001) 477, for daily marches of 20 to 30 km; Chevallier, R., Roman roads (London 1976) 194. Ancient sources tend to privilege particularly rapid marches (for which see Riepl, W., Das Nachrichtenwesen des Altertums [Leipzig 1913] 129–36) that cannot reflect routine standards and longer-distance performance (pace Laurence [supra n.10] 82). For determining distances, ORBIS relies on road lengths measured by GIS. Comparison between measured distances and those reported in various Roman itineraries has revealed substantial incongruities that cast doubt on the latter's accuracy. Thus, the matches between measured distances and itinerary data for NW Spain observed by J. L. V. González, “GIS and Roman ways research in Hispania” (a paper presented at the ESRI European User Conference in 2011 at Madrid) could not be replicated for the system as a whole: see D.-E. Padilla Peralta, “ORBIS and the ancient itineraries: preliminary observations,” ORBIS/Applying ORBIS, at Cf. also Pazarli, M., Livieratos, E. and Boutoura, C., “Road network of Crete in Tabula Peutingeriana,” e-Perimetron 2 (2007) 245–60.

23 For an interactive ‘proof-of-concept’ version, see ORBIS/Mapping ORBIS/Interactive Distance Cartogram,, and subsequently Version 2.0 of ORBIS. Cartograms are particularly useful in combatting what has been called “the first law of cognitive geography”, which holds that observers believe that objects are more similar the closer together they are: Montello, D. R., Fabrikant, S. I., Ruocco, M. and Middleton, R. S., “Testing the first law of cognitive geography on point-display spatializations,” in Kuhn, W., Worboys, M. F. and Timpf, S. (edd.), Spatial information theory: foundations of Geographic Information Science. Proc. conf. COSIT '03 (Berlin 2003) 316–31.

24 The literature on the speed of Roman messengers is large: the most substantial discussions are Ramsay, A. M., “The speed of the Roman imperial post,” JRS 15 (1925) 6074; Stoffel, P., Über die Staatspost, die Ochsengespanne und die requirierten Ochsengespanne (Bern 1994) 161–65, and now especially Kolb (supra n.22) 321-32. Normal messenger speeds gathered by these studies fall in a range from the 50s to the 80s km per day, for a median value of 67 km (45 Roman miles). Cf. also McCormick (supra n.22) 476-77 (45-78 km per day); Renouard, Y., “Routes, étapes et vitesses de marche de France à Rome au XIIIe et au XIVe siècles d'après les itinéraires d'Eudes Rigaud (1254) et de Barthélemy Bonis (1350),” in Studi in onore di Amintore Fanfani, vol. 3 (Milan 1962) 113 (50-80 km per day in 15th-c. Europe). Again, higher speeds are documented (Kolb ibid. 322) but were not the standard (pace Laurence [supra n.10] 81, who generally seeks to maximize Roman travel performance). I have used (supra n.11) 67 km per day as an approximation of the mean speed of the cursus publicus. For military row boats, I draw on Zos. 2.10.2-3 and the experimental re-creation by Himmler, Konen and Löffl (supra n.21), for a daily speed of 120 km downriver and 50 km upriver. The extent to which sea-going ships were used by the cursus publicus remains highly uncertain: cf. Reddé (supra n.19) 447-51.

25 For the underlying price rates, see supra n.8.

26 The simulations in ORBIS assume that regular sailing was not feasible in parts of the ocean where wave heights of at least 12 feet are encountered for at least 10% of the time in a given month, a condition that serves as a proxy of stormy weather: National Imagery and Mapping Agency, Atlas of pilot charts: North Atlantic Ocean (2002). In the Roman world, such weather events were limited to the Atlantic and, in the winter, the NW Mediterranean to the south of France.

27 Ramsay, W. M., “Roads and travel,” in Hastings, J. (ed.), A dictionary of the Bible, extra volume (New York 1904) 376; Goitein, S. D., A Mediterranean society: the Jewish communities of the world as portrayed in the documents of the Cairo Geniza, I (Berkeley, CA 1967) 316–17; Leighton, A. C., Transport and communication in Early Medieval Europe AD 500-1100 (Newton Abbot 1972) 132; Meijer, F. J., “Mare clausum aut mare apertum: een beschouwing over zeevart in de winter,” Hermeneus 55 (1983) 220; Ohler, N., The medieval traveler (Woodbridge 1989) 11; Jehel, G., Les Génois en Méditerranée occidentale (fin XI-début du XIV siècle) (Paris 1993) 315–16; Braudel (supra n.2) 227-32; Horden, P. and Purcell, N., The corrupting sea: a study of Mediterranean history (Oxford 2000) 137–43; McCormick (supra n.22) 444-68.

28 Sweeping claims about winter closures of roads (albeit mostly in the mountains: W. M. Ramsay [supra n.27] 377; Vigneron [supra n.22]) conflict with comparative historical data for speedy Alpine crossings and even fairs in the depths of winter. See Renouard (supra n.24) 411-20; Bergier, J. F., “Le trafic à travers les Alpes et les liaisons transalpines du Haut Moyen Âge aux XVIIe siècle,” in Le Alpi et l'Europe, vol. 3 (Bari 1975) 37; Castelnuovo, G., “Tempi, distanze e percorsi in montagna nel basso medioevo,” in Spazi, tempi, misure e percorsi nell'Europa del bassomedioevo (Spoleto 1996) 226–27.

29 The classic discussions of the Po valley all, to varying degrees, stress its isolation: Brunt, P. A., Italian manpower 225 B.C.-A.D. 14 (Oxford 1971) 172–84; Garnsey, P. (ed. Scheidel, W.), Cities, peasants and food in classical antiquity (Cambridge 1998) 4562; Harris, W. V., Rome's imperial economy (Oxford 2011) 188–97. Cf. also Horden and Purcell (supra n.27) 115-22 for “dispersed hinterlands” more generally.

30 Contra, e.g., Hopkins, K., Conquerors and slaves (Cambridge 1978) 6869; Cascio, E. Lo, “The size of the Italian population: Beloch and the meaning of the Italian census figures,” JRS 84 (1994) 39; Morley, N., Metropolis and hinterland (Cambridge 1996) 182; Cascio, E. Lo, “The population of Roman Italy in town and country,” in Bintliff, J. and Sbonias, K. (edd.), Reconstructing past population trends in Mediterranean Europe (Oxford 1999) 164–65; see already Scheidel, W., “Roman population size: the logic of the debate,” in Ligt, L. de and Northwood, S. (edd.), People, land, and politics (Leiden 2008) 32.

31 Its current was stronger than those of other major rivers in the empire (e.g., Beardmore, N., Manual of hydrology [London 1872] 158) and could be reinforced by the Mistral, which blows roughly from the north. In the Middle Ages, a flat barge could reach Avignon from Lyon in 2-5 days, but might take a month to be towed back upriver: Ohler (supra n.27) 34. In addition, the river ran low for part of the year: Brewster, D., “Inland navigation,” in The Edinburgh encyclopaedia vol. 14 (1832) 265; Denel, F., “La navigation sur le Rhône au XVe siècle d'après les registres de péage de Baix,” Annales du Midi 82 (1970) 289–90.

32 For the boundaries of olive cultivation, see Horden and Purcell (supra n.27) 14; for its importance in the Roman world, see most recently Woolf, G., Rome: an empire's story (New York 2012) 51. Along with W. V. Harris (“The Mediterranean and ancient history,” in id. [ed.], Rethinking the Mediterranean [Oxford 2005]), I think of the Mediterranean in terms of a construct “with something of a natural basis” (4) represented by climate, certain crops and styles of animal husbandry, and relatively easy maritime navigability (21-23), notwithstanding Horden and Purcell's emphasis on micro-ecological fragmentation.

33 It is worth noting that the attempted conquest of Germany (12 B.C.-A.D. 9/16), Trajan's invasion of Armenia and Mesopotamia (A.D. 114-117), and Roman campaigning in Bohemia, Moravia, Slovakia and the Hungarian plain, which may or may not have aimed at conquest (A.D. 172180), took place at exceptionally remote locations as defined by connectivity costs relative to the imperial capital; the odds for successful incorporation were small by that standard alone. Dacia, shielded by the Carpathians, remained the sole exception, and it was the first established Roman province to be abandoned.

34 Aside from isolated instances of naval support for military crossings of the Strait of Otranto or the Bosporus/Dardanelles, and even rarer operations involving N Africa, significant troop transfers by sea seem virtually unknown in civil-war contexts of the monarchical period: cf. Starr (supra n.19) 182-83 and 190; Reddé (supra n.19) 373.

35 Though not to the rest of the empire; this is a result of the high time-costs of negotiating entry into the Black Sea, which a more realistic model would have to factor into price simulations as well: see de Marigny, E. Taitbout, New sailing directions of the Dardanelles, Marmara Sea, Bosphorus, Black Sea, and the Sea of Azov (London 1847, and especially Labaree, B. W., “How the Greeks sailed into the Black Sea,” AJA 26 (1957) 32. Weaker effects in the Dardanelles made the Aegean more ‘distant’ than it would seem from a conventional map.

36 This is consistent with the parabolical trajectory of the growth and decline of empires: Motyl, A. J., Imperial ends: the decay, collapse, and revival of empires (New York 2001) 7.

37 On this entity, see Drinkwater, J. F., The Gallic Empire (Stuttgart 1987) especially 19 fig. 1.1 on its SW frontier.

38 For the problem, see, e.g., Morley, N., “The early Roman empire: distribution,” in Scheidel, W., Morris, I. and Saller, R. (edd.), The Cambridge economic history of the Greco-Roman world (Cambridge 2007) 580–87; for the current state of the debate, see the Forum on Roman trade” in Scheidel, W. (ed.), The Cambridge companion to the Roman economy (Cambridge 2012) 287317.

39 For a somewhat more detailed summary, see W. Scheidel, “Approaching the Roman economy,” in id. (ed.) 2012 (supra n.38) 8-9. For the former view, which dates back to E. Meyer and M. Rostovtzeff, see especially von Freyberg, H.-U., Kapitalverkehr und Handel im römischen Kaiserreich (27 v. Chr.-235 n. Chr.) (Freiburg 1989); Silver, M., “Roman economic growth and living standards: perceptions versus evidence,” AncSoc 37 (2007) 191252; id., “Historical otherness, the Roman bazaar, and primitivism: P. F. Bang on the Roman economy,” JRA 22 (2009) 421-43; Temin, P., The Roman market economy (Princeton, NJ 2013). For the latter view, see Hopkins, K., “Taxes and trade in the Roman empire (200 B.C.-A.D. 400),” JRS 70 (1980) 101–25; id., “Rome, taxes, rents and trade,” Kodai 6-7 (1995-96) 41-75 (reprinted in W. Scheidel and S. von Reden [edd.], The ancient economy [Edinburgh 2002] 190-230); Wickham, C., Framing the Early Middle Ages: Europe and the Mediterranean, 400-800 (Oxford 2005); Bang, P. F., “Trade and empire – in search of organizing concepts for the Roman economy,” P&P 195 (2007) 354; id., The Roman bazaar: a comparative study of trade and markets in a tributary empire (Cambridge 2008).

40 For early attempts, see Carreras 2000 (supra n.16) and “An archaeological perspective” (supra n.16). See now especially Brughmans, T., “Connecting the dots: towards archaeological network analysis,” OJA 29 (2010) 277303, and J. Remesal Rodriguez's project “EPNet: Production and distribution of food during the Roman empire: economics and political dynamics”, which was awarded an ERC Advanced Grant in 2013. More generally, cf. Knappet, C., Network analysis in archaeology: new approaches to regional interaction (Oxford 2013).

41 Finley, M. I., The ancient economy (updated edn.; Berkeley, CA 1999) 22; Temin, P., “A market economy in the Early Roman empire,” JRS 91 (2001) 169–81; cf. also: The economy of the Early Roman empire,” J. Economic Perspectives 20 (2006) 133–51.

42 Kessler, D. and Temin, P., “Money and prices in the Early Roman empire,” in Harris, W. V. (ed.), The monetary systems of the Greeks and Romans (Oxford 2008) 137–59, reiterated in Temin (supra n.39) 29-52. The sites are Sicily, the Po valley, Lusitania, Pisidian Antioch, the Fayyum, and Palestine. In this scenario, physical distance from Rome accounts for 79% of variance in local grain prices.

43 Bransbourg, G., “Rome and the economic integration of empire,” ISAW Working Papers 3, available at

44 Sites from Bransbourg (ibid.) Table 3, for which see prices and estimated period-specific price differentials to Rome. Coastal Mediterranean sites: Sicily (0.84 from Syracuse), Pompeii (0.43), Fayyum (3.59 via the Nile), Palestine (2.78 from Ascalon), Forum Sempronii (1.54 via Fanum Fortunae), Lanuvium (1.2), Tarracina (0.31). Others: Lusitania (2.2 from Olisipo), Po valley (2.67 from Placentia), Antioch in Pisidia (6.6), Veleia (3.44), Sicca Veneria (3.93 routed by road to the nearest port of Thabraca, unlike via Carthage as in ORBIS).

45 This new finding is important not least because Bransbourg's results allowed Temin (supra n.39) 52 to interpret them as support for his own thesis, contrary to Bransbourg's overall argument.

46 In this context it does not matter who bore these costs: even in the case of coerced transfers, the State could not make them disappear simply by unloading them onto subjects liable to transport liturgies. Connectivity cost put strain on the system regardless of whether it raised State expenditure (if it was directly covered by the State) or whether it raised enforcement costs and reduced overall output (if it was borne by taxpayers).

48 Pleiades ( already allows us to locate over 34,000 ancient sites.

50 See Blondel, V. D., Guillaume, J.-L., Lambiotte, R. and Lefebvre, E., “Fast unfolding of communities in large networks,” J. Statistical Mechanics: theory and experiment 10 (2008) P10008, doi:10.1088/1742-5468/2008/10/P10008; R. Lambiotte, J.-C. Delvenne and M. Barahona, “Laplacle dynamics and multiscale modular structure in networks,” arXiv:0812.1170v3 [] (2009). I owe these references to E. Meeks.

51 For network analysis based on the itineraria, see Graham, S., “Networks, agent-based models and the Antonine itineraries: implications for Roman archaeology,” J. Medit. Arch. 19 (2006) 4564; Isaksen, L., “The application of network analysis to ancient transport geography: a case study of Roman Baetica,” Digital Medievalist 4 (2008),

52 “Modeling points the way to a computing that is of as well as in the humanities: a continual process of coming to know by manipulating representations”: McCarthy, W., “Modeling: a study in words and meanings,” in Schreibman, S., Siemens, R. and Unsworth, J. (edd.), A companion to digital humanities (2004), Note its potential to tie in with larger concerns such as the Digital Earth movement: e.g., Craglia, al., “Digital Earth 2020: towards the vision for the next decade,” Int. J. Digital Earth 5.1 (2012) 421, especially 13-14.

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